<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019d1bb6-6fd5-7124-a286-725bc7bc1c18,g:66208453-bddc-4f16-92ca-9c3289e9e3fa-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.ui.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="ubnt-20260331.xsd#ConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019d1bb6-7090-71cf-98c7-a36b61c0c75d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019d1bb6-7090-72c7-9b80-d7fed6e52930" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-71cf-98c7-a36b61c0c75d" xlink:to="loc_us-gaap_StatementTable_019d1bb6-7090-72c7-9b80-d7fed6e52930" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019d1bb6-7090-77f5-a31c-defa35cb5fb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019d1bb6-7090-72c7-9b80-d7fed6e52930" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019d1bb6-7090-77f5-a31c-defa35cb5fb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d1bb6-7090-77f5-a31c-defa35cb5fb7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d1bb6-7090-77f5-a31c-defa35cb5fb7" xlink:to="loc_us-gaap_EquityComponentDomain_019d1bb6-7090-77f5-a31c-defa35cb5fb7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d1bb6-7090-7e33-9c0c-0c36eca1e9cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d1bb6-7090-77f5-a31c-defa35cb5fb7" xlink:to="loc_us-gaap_EquityComponentDomain_019d1bb6-7090-7e33-9c0c-0c36eca1e9cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019d1bb6-7090-7e93-a077-f050f1b7144b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d1bb6-7090-7e33-9c0c-0c36eca1e9cc" xlink:to="loc_us-gaap_CommonStockMember_019d1bb6-7090-7e93-a077-f050f1b7144b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019d1bb6-7090-768e-aeaf-a4a532ae19c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d1bb6-7090-7e33-9c0c-0c36eca1e9cc" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019d1bb6-7090-768e-aeaf-a4a532ae19c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019d1bb6-7090-71d9-a55e-d5eb29bbd39e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d1bb6-7090-7e33-9c0c-0c36eca1e9cc" xlink:to="loc_us-gaap_RetainedEarningsMember_019d1bb6-7090-71d9-a55e-d5eb29bbd39e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-71cf-98c7-a36b61c0c75d" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019d1bb6-7090-7681-afe9-c0f6b859f9e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019d1bb6-7090-7681-afe9-c0f6b859f9e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019d1bb6-7090-724a-a100-5f651fe9f2d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:to="loc_us-gaap_StockholdersEquity_019d1bb6-7090-724a-a100-5f651fe9f2d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019d1bb6-7090-7900-a221-a62768e76376" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:to="loc_us-gaap_NetIncomeLoss_019d1bb6-7090-7900-a221-a62768e76376" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019d1bb6-7090-709f-87c8-0777ce0dc87b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019d1bb6-7090-709f-87c8-0777ce0dc87b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_019d1bb6-7090-7fab-bec3-88a166f6af98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_019d1bb6-7090-7fab-bec3-88a166f6af98" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019d1bb6-7090-79a5-87bc-ee5413ae1032" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019d1bb6-7090-79a5-87bc-ee5413ae1032" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_019d1bb6-7090-704d-812b-315fb9dbde84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019d1bb6-7090-7cab-85b0-b8262542da78" xlink:to="loc_us-gaap_DividendsCommonStockCash_019d1bb6-7090-704d-812b-315fb9dbde84" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019d1bb6-7090-727a-bad1-e1b7a027601f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019d1bb6-7090-784e-a898-1eb74fba9c62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/ConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="ubnt-20260331.xsd#ConsolidatedStatementsofCashFlows"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/ConsolidatedStatementsofCashFlows" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019d1bb6-7090-7bdb-b7f9-4ecfd012f0cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:to="loc_us-gaap_StatementTable_019d1bb6-7090-7bdb-b7f9-4ecfd012f0cb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-7ff0-846f-5e30914f9f09" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019d1bb6-7090-7bdb-b7f9-4ecfd012f0cb" xlink:to="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-7ff0-846f-5e30914f9f09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7ff0-846f-5e30914f9f09_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-7ff0-846f-5e30914f9f09" xlink:to="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7ff0-846f-5e30914f9f09_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7703-9b31-5b5deac69213" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-7ff0-846f-5e30914f9f09" xlink:to="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7703-9b31-5b5deac69213" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019d1bb6-7090-7bf8-b861-7d1748b877e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7703-9b31-5b5deac69213" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019d1bb6-7090-7bf8-b861-7d1748b877e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_TermLoanMember_019d1bb6-7090-7823-8d02-3a0e1a3d9942" xlink:href="ubnt-20260331.xsd#ubnt_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7703-9b31-5b5deac69213" xlink:to="loc_ubnt_TermLoanMember_019d1bb6-7090-7823-8d02-3a0e1a3d9942" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-7ff8-a2b8-db6ca758143b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-7ff8-a2b8-db6ca758143b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019d1bb6-7090-740c-997a-e18834dc3195" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-7ff8-a2b8-db6ca758143b" xlink:to="loc_us-gaap_NetIncomeLoss_019d1bb6-7090-740c-997a-e18834dc3195" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-7ff8-a2b8-db6ca758143b" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019d1bb6-7090-7f2e-8f2e-5b0400a6b54a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019d1bb6-7090-7f2e-8f2e-5b0400a6b54a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_019d1bb6-7090-7bb0-83b9-9b79c753366f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_019d1bb6-7090-7bb0-83b9-9b79c753366f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_OperatingLeaseNonCashLeaseExpense_019d1bb6-7090-7678-a41b-afa0be5bdeb5" xlink:href="ubnt-20260331.xsd#ubnt_OperatingLeaseNonCashLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_ubnt_OperatingLeaseNonCashLeaseExpense_019d1bb6-7090-7678-a41b-afa0be5bdeb5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWriteDown_019d1bb6-7090-76de-858c-95298f8627d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InventoryWriteDown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_us-gaap_InventoryWriteDown_019d1bb6-7090-76de-858c-95298f8627d0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ProvisionforGainLossonVendorDeposit_019d1bb6-7090-7e82-b52f-f2e47e6c345d" xlink:href="ubnt-20260331.xsd#ubnt_ProvisionforGainLossonVendorDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_ubnt_ProvisionforGainLossonVendorDeposit_019d1bb6-7090-7e82-b52f-f2e47e6c345d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019d1bb6-7090-7e13-9dab-8894996dd27e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_us-gaap_ShareBasedCompensation_019d1bb6-7090-7e13-9dab-8894996dd27e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019d3c74-577b-765e-8a4e-833cfa1e5e73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019d3c74-577b-765e-8a4e-833cfa1e5e73" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_019dbda5-dd40-77a9-9969-4b62cff4965b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProvisionForDoubtfulAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_019dbda5-dd40-77a9-9969-4b62cff4965b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncashIncomeExpense_019d1bb6-7090-7dbf-8fdd-22738f298a04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncashIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_us-gaap_OtherNoncashIncomeExpense_019d1bb6-7090-7dbf-8fdd-22738f298a04" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-763f-a076-10f3251a88ef" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_019d1bb6-7090-7842-a35f-7953c2cec16c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_019d1bb6-7090-7842-a35f-7953c2cec16c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_019d1bb6-7090-76b2-b1e7-537f74b5d3f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInInventories"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_019d1bb6-7090-76b2-b1e7-537f74b5d3f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_IncreaseDecreaseinVendorDeposits_019d1bb6-7090-7f35-be2e-15edadba6ebd" xlink:href="ubnt-20260331.xsd#ubnt_IncreaseDecreaseinVendorDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:to="loc_ubnt_IncreaseDecreaseinVendorDeposits_019d1bb6-7090-7f35-be2e-15edadba6ebd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019d1bb6-7090-7a5d-bdbc-d4134f7d6d88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019d1bb6-7090-7a5d-bdbc-d4134f7d6d88" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019d1bb6-7090-7d97-aff6-00b0fc5aaffe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019d1bb6-7090-7d97-aff6-00b0fc5aaffe" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_019d1bb6-7090-7d2c-97fe-170cd2062caf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_019d1bb6-7090-7d2c-97fe-170cd2062caf" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_019d1bb6-7090-7d01-a852-aa95bb4ddd89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_019d1bb6-7090-7d01-a852-aa95bb4ddd89" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities_019d1bb6-7090-765b-9e3a-71e5940f6430" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019d1bb6-7090-7701-8a2b-69edd557f24e" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities_019d1bb6-7090-765b-9e3a-71e5940f6430" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019d1bb6-7090-77a4-a87f-ea3a763ab5bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019d1bb6-7090-7ff8-a2b8-db6ca758143b" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019d1bb6-7090-77a4-a87f-ea3a763ab5bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019d1bb6-7090-7f2f-9130-81fcf719540f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019d1bb6-7090-7f2f-9130-81fcf719540f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019d1bb6-7090-7407-8874-8c6a8a8473d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019d1bb6-7090-7f2f-9130-81fcf719540f" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019d1bb6-7090-7407-8874-8c6a8a8473d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019d1bb6-7090-7509-a42e-ad963b154cc0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019d1bb6-7090-7f2f-9130-81fcf719540f" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019d1bb6-7090-7509-a42e-ad963b154cc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019d1bb6-7090-7ba9-9aea-5aea771976f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019d1bb6-7090-7ba9-9aea-5aea771976f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_019d3c75-d6d6-7027-9d51-9b3121fd34f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromLongTermLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019d1bb6-7090-7ba9-9aea-5aea771976f9" xlink:to="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_019d3c75-d6d6-7027-9d51-9b3121fd34f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_RepaymentofLongTermLinesofCreditPrincipal_019d1bb6-7090-7609-b070-58cf8b3dd498" xlink:href="ubnt-20260331.xsd#ubnt_RepaymentofLongTermLinesofCreditPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019d1bb6-7090-7ba9-9aea-5aea771976f9" xlink:to="loc_ubnt_RepaymentofLongTermLinesofCreditPrincipal_019d1bb6-7090-7609-b070-58cf8b3dd498" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_019d1bb6-7090-741b-bf8f-ca10e4e21826" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019d1bb6-7090-7ba9-9aea-5aea771976f9" xlink:to="loc_us-gaap_PaymentsOfDividends_019d1bb6-7090-741b-bf8f-ca10e4e21826" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_019d1bb6-7090-7474-ab23-a2ac680dabee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019d1bb6-7090-7ba9-9aea-5aea771976f9" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_019d1bb6-7090-7474-ab23-a2ac680dabee" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019d1bb6-7090-71f4-8d00-1ccb1182fa4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019d1bb6-7090-7ba9-9aea-5aea771976f9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019d1bb6-7090-71f4-8d00-1ccb1182fa4a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019d1bb6-7090-7239-886c-cbb82bf28470" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019d1bb6-7090-7239-886c-cbb82bf28470" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019d1bb6-7090-744d-810f-6f7deb0f8e0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019d1bb6-7090-744d-810f-6f7deb0f8e0f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019d1bb6-7090-7bc1-9236-f5110a812eea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_019d1bb6-7090-774d-899d-129144b4877c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_019d1bb6-7090-774d-899d-129144b4877c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_019d1bb6-7090-797a-b57a-b3cb5e914a15" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_019d1bb6-7090-774d-899d-129144b4877c" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_019d1bb6-7090-797a-b57a-b3cb5e914a15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_019d1bb6-7090-76cf-b747-7fb754700fe9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_019d1bb6-7090-774d-899d-129144b4877c" xlink:to="loc_us-gaap_InterestPaidNet_019d1bb6-7090-76cf-b747-7fb754700fe9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019d1bb6-7090-7fa7-bb8e-402efefde4b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019d1bb6-7090-75db-a377-0dd832ac7069" xlink:to="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019d1bb6-7090-7fa7-bb8e-402efefde4b5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_019d1bb6-7090-78fe-836b-cfefb7c38c45" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019d1bb6-7090-7fa7-bb8e-402efefde4b5" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_019d1bb6-7090-78fe-836b-cfefb7c38c45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019d1bb6-7090-76fc-99a6-ab005ab6cba5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019d1bb6-7090-7fa7-bb8e-402efefde4b5" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019d1bb6-7090-76fc-99a6-ab005ab6cba5" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/REVENUESDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#REVENUESDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/REVENUESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019d1bb6-7090-7ca8-a15b-2e5b27b9df6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d1bb6-7090-7268-b07f-19d7c914220a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019d1bb6-7090-7ca8-a15b-2e5b27b9df6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d1bb6-7090-7268-b07f-19d7c914220a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019d1bb6-7090-7708-9e53-31f8d31266a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d1bb6-7090-7268-b07f-19d7c914220a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019d1bb6-7090-7708-9e53-31f8d31266a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019d1bb6-7090-79c9-b585-2a961b90a6af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019d1bb6-7090-7ca8-a15b-2e5b27b9df6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019d1bb6-7090-79c9-b585-2a961b90a6af" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/REVENUESDetails_1" xlink:type="simple" xlink:href="ubnt-20260331.xsd#REVENUESDetails_1"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/REVENUESDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019d1bb6-7090-7ca8-a15b-2e5b27b9df6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d1bb6-7090-7268-b07f-19d7c914220a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019d1bb6-7090-7ca8-a15b-2e5b27b9df6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019d1bb6-7090-7268-b07f-19d7c914220a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019d1bb6-7090-79c9-b585-2a961b90a6af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019d1bb6-7090-7ca8-a15b-2e5b27b9df6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019d1bb6-7090-79c9-b585-2a961b90a6af" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/EARNINGSPERSHAREDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#EARNINGSPERSHAREDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/EARNINGSPERSHAREDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-7090-700d-9f90-f4bd6bdf16bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-7090-7590-ad29-aad9a8314828" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-7090-700d-9f90-f4bd6bdf16bf" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-7090-7590-ad29-aad9a8314828" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019d1bb6-7090-768e-a66c-cde104ec4763" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-7090-7590-ad29-aad9a8314828" xlink:to="loc_us-gaap_AwardTypeAxis_019d1bb6-7090-768e-a66c-cde104ec4763" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-7090-768e-a66c-cde104ec4763_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019d1bb6-7090-768e-a66c-cde104ec4763" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-7090-768e-a66c-cde104ec4763_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-7090-71ee-ae12-189fb93d976c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019d1bb6-7090-768e-a66c-cde104ec4763" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-7090-71ee-ae12-189fb93d976c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019d1bb6-7090-728d-a4ab-5b2d001cd814" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-7090-71ee-ae12-189fb93d976c" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019d1bb6-7090-728d-a4ab-5b2d001cd814" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract_019d1bb6-7090-7ff6-90d7-4fa093d03e63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-7090-700d-9f90-f4bd6bdf16bf" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract_019d1bb6-7090-7ff6-90d7-4fa093d03e63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019d1bb6-7090-73a9-af6b-fead229cf8dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract_019d1bb6-7090-7ff6-90d7-4fa093d03e63" xlink:to="loc_us-gaap_NetIncomeLoss_019d1bb6-7090-73a9-af6b-fead229cf8dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019d1bb6-7090-7fc4-bbdf-11aa0762d44e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-7090-700d-9f90-f4bd6bdf16bf" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019d1bb6-7090-7fc4-bbdf-11aa0762d44e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019d1bb6-7090-7c00-8c93-d6b01e0712c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019d1bb6-7090-7fc4-bbdf-11aa0762d44e" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019d1bb6-7090-7c00-8c93-d6b01e0712c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_019d1bb6-7090-7717-8975-57ed5c3999fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019d1bb6-7090-7fc4-bbdf-11aa0762d44e" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_019d1bb6-7090-7717-8975-57ed5c3999fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019d1bb6-7090-7b81-a321-d684ff4e5ccd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_019d1bb6-7090-7717-8975-57ed5c3999fc" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019d1bb6-7090-7b81-a321-d684ff4e5ccd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019d1bb6-7090-79bf-936a-b5957d2130e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-7090-700d-9f90-f4bd6bdf16bf" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019d1bb6-7090-79bf-936a-b5957d2130e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareReconciliationAbstract_019d1bb6-7090-7e6c-bbd9-9d6306448eeb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareReconciliationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-7090-700d-9f90-f4bd6bdf16bf" xlink:to="loc_us-gaap_EarningsPerShareReconciliationAbstract_019d1bb6-7090-7e6c-bbd9-9d6306448eeb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019d1bb6-7090-7187-8794-09592d48e8d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_019d1bb6-7090-7e6c-bbd9-9d6306448eeb" xlink:to="loc_us-gaap_EarningsPerShareBasic_019d1bb6-7090-7187-8794-09592d48e8d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019d1bb6-7090-70d4-8177-f46a5f4404f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_019d1bb6-7090-7e6c-bbd9-9d6306448eeb" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019d1bb6-7090-70d4-8177-f46a5f4404f5" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/BALANCESHEETCOMPONENTSScheduleofPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#BALANCESHEETCOMPONENTSScheduleofPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/BALANCESHEETCOMPONENTSScheduleofPropertyandEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019d1bb6-7090-7a99-a554-37ff089f8868" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019d1bb6-7090-7224-ba21-d4424ecc869d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019d1bb6-7090-7a99-a554-37ff089f8868" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019d1bb6-7090-7224-ba21-d4424ecc869d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019d1bb6-7090-723c-a936-2d221c2cd5fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019d1bb6-7090-7224-ba21-d4424ecc869d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019d1bb6-7090-723c-a936-2d221c2cd5fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-723c-a936-2d221c2cd5fb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019d1bb6-7090-723c-a936-2d221c2cd5fb" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-723c-a936-2d221c2cd5fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019d1bb6-7090-723c-a936-2d221c2cd5fb" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_TestingEquipmentMember_019d1bb6-7090-7ef2-98a8-aa692e8fd44d" xlink:href="ubnt-20260331.xsd#ubnt_TestingEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:to="loc_ubnt_TestingEquipmentMember_019d1bb6-7090-7ef2-98a8-aa692e8fd44d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ToolingEquipmentMember_019d1bb6-7090-7f79-a9fc-0669441a7d55" xlink:href="ubnt-20260331.xsd#ubnt_ToolingEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:to="loc_ubnt_ToolingEquipmentMember_019d1bb6-7090-7f79-a9fc-0669441a7d55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019d1bb6-7090-768c-a7eb-c8eb0ca4c16f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019d1bb6-7090-768c-a7eb-c8eb0ca4c16f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ComputerAndOtherEquipmentMember_019d1bb6-7090-781d-8666-c94b10c3bee5" xlink:href="ubnt-20260331.xsd#ubnt_ComputerAndOtherEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:to="loc_ubnt_ComputerAndOtherEquipmentMember_019d1bb6-7090-781d-8666-c94b10c3bee5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019d1bb6-7090-728a-a168-a7b859f38ae2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019d1bb6-7090-728a-a168-a7b859f38ae2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019d1bb6-7090-72ef-8f09-903010c552ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019d1bb6-7090-72ef-8f09-903010c552ac" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirTransportationEquipmentMember_019d1bb6-7090-72b0-8ffb-59045144968a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AirTransportationEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019d1bb6-7090-702e-869a-16a6d404d45d" xlink:to="loc_us-gaap_AirTransportationEquipmentMember_019d1bb6-7090-72b0-8ffb-59045144968a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019d1bb6-7090-7c1f-be07-335f287ea97c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019d1bb6-7090-7a99-a554-37ff089f8868" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019d1bb6-7090-7c1f-be07-335f287ea97c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019d1bb6-7090-7857-9912-5c16f764f5f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019d1bb6-7090-7a99-a554-37ff089f8868" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019d1bb6-7090-7857-9912-5c16f764f5f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019d1bb6-7090-75d9-be19-b3458d3f29ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019d1bb6-7090-7a99-a554-37ff089f8868" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019d1bb6-7090-75d9-be19-b3458d3f29ea" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/ACCRUEDWARRANTYNarrativeDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#ACCRUEDWARRANTYNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/ACCRUEDWARRANTYNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductWarrantyLiabilityLineItems_019d1bb6-7090-76cb-8839-23df7de09780" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductWarrantyLiabilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductWarrantyLiabilityTable_019d1bb6-7090-7946-b37c-ac6ee4cc5556" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductWarrantyLiabilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ProductWarrantyLiabilityLineItems_019d1bb6-7090-76cb-8839-23df7de09780" xlink:to="loc_us-gaap_ProductWarrantyLiabilityTable_019d1bb6-7090-7946-b37c-ac6ee4cc5556" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d1bb6-7090-76c1-9b0f-2b2eb6786773" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ProductWarrantyLiabilityTable_019d1bb6-7090-7946-b37c-ac6ee4cc5556" xlink:to="loc_srt_RangeAxis_019d1bb6-7090-76c1-9b0f-2b2eb6786773" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d1bb6-7090-76c1-9b0f-2b2eb6786773_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019d1bb6-7090-76c1-9b0f-2b2eb6786773" xlink:to="loc_srt_RangeMember_019d1bb6-7090-76c1-9b0f-2b2eb6786773_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d1bb6-7090-76c2-b4ed-15111cca7aca" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019d1bb6-7090-76c1-9b0f-2b2eb6786773" xlink:to="loc_srt_RangeMember_019d1bb6-7090-76c2-b4ed-15111cca7aca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019d1bb6-7090-7069-9f2e-1f5c10763685" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d1bb6-7090-76c2-b4ed-15111cca7aca" xlink:to="loc_srt_MinimumMember_019d1bb6-7090-7069-9f2e-1f5c10763685" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019d1bb6-7090-7149-83f8-4ee3c414e6f6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d1bb6-7090-76c2-b4ed-15111cca7aca" xlink:to="loc_srt_MaximumMember_019d1bb6-7090-7149-83f8-4ee3c414e6f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerSalesChannelAxis_019d1bb6-7090-74a3-b55c-b13052391e5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerSalesChannelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ProductWarrantyLiabilityTable_019d1bb6-7090-7946-b37c-ac6ee4cc5556" xlink:to="loc_us-gaap_ContractWithCustomerSalesChannelAxis_019d1bb6-7090-74a3-b55c-b13052391e5e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerSalesChannelDomain_019d1bb6-7090-74a3-b55c-b13052391e5e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerSalesChannelDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelAxis_019d1bb6-7090-74a3-b55c-b13052391e5e" xlink:to="loc_us-gaap_ContractWithCustomerSalesChannelDomain_019d1bb6-7090-74a3-b55c-b13052391e5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerSalesChannelDomain_019d1bb6-7090-7389-9c4e-af646a87e5c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerSalesChannelDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelAxis_019d1bb6-7090-74a3-b55c-b13052391e5e" xlink:to="loc_us-gaap_ContractWithCustomerSalesChannelDomain_019d1bb6-7090-7389-9c4e-af646a87e5c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesChannelThroughIntermediaryMember_019d1bb6-7090-7904-b852-8c57650a079f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesChannelThroughIntermediaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelDomain_019d1bb6-7090-7389-9c4e-af646a87e5c9" xlink:to="loc_us-gaap_SalesChannelThroughIntermediaryMember_019d1bb6-7090-7904-b852-8c57650a079f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesChannelDirectlyToConsumerMember_019d1bb6-7090-740a-9dab-61ace1ed8cde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesChannelDirectlyToConsumerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelDomain_019d1bb6-7090-7389-9c4e-af646a87e5c9" xlink:to="loc_us-gaap_SalesChannelDirectlyToConsumerMember_019d1bb6-7090-740a-9dab-61ace1ed8cde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_StandardProductWarrantyPeriod_019d1bb6-7090-7f00-bf0a-b423fa573f83" xlink:href="ubnt-20260331.xsd#ubnt_StandardProductWarrantyPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductWarrantyLiabilityLineItems_019d1bb6-7090-76cb-8839-23df7de09780" xlink:to="loc_ubnt_StandardProductWarrantyPeriod_019d1bb6-7090-7f00-bf0a-b423fa573f83" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/DEBTNarrativeDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#DEBTNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/DEBTNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-716f-b59c-e33560d21e07" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-716f-b59c-e33560d21e07" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-7f5f-abab-bf2eb428d46e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-716f-b59c-e33560d21e07" xlink:to="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-7f5f-abab-bf2eb428d46e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7f5f-abab-bf2eb428d46e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-7f5f-abab-bf2eb428d46e" xlink:to="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7f5f-abab-bf2eb428d46e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-718d-a19b-d176d700a173" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-7f5f-abab-bf2eb428d46e" xlink:to="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-718d-a19b-d176d700a173" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019d1bb6-7090-7f71-a8bd-b8c36a769bb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-718d-a19b-d176d700a173" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019d1bb6-7090-7f71-a8bd-b8c36a769bb3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_InitialTermLoanMember_019d1bb6-7090-73a1-a756-23f09e00c5c3" xlink:href="ubnt-20260331.xsd#ubnt_InitialTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-718d-a19b-d176d700a173" xlink:to="loc_ubnt_InitialTermLoanMember_019d1bb6-7090-73a1-a756-23f09e00c5c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_019d1bb6-7090-7a13-a7db-4e0cf7a1ba43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-718d-a19b-d176d700a173" xlink:to="loc_us-gaap_LetterOfCreditMember_019d1bb6-7090-7a13-a7db-4e0cf7a1ba43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_SwinglineLoanMember_019d1bb6-7090-7498-ad06-0cce75e9ca77" xlink:href="ubnt-20260331.xsd#ubnt_SwinglineLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-718d-a19b-d176d700a173" xlink:to="loc_ubnt_SwinglineLoanMember_019d1bb6-7090-7498-ad06-0cce75e9ca77" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_TermLoanMember_019d1bb6-7090-7722-baf0-6f7c4a158a87" xlink:href="ubnt-20260331.xsd#ubnt_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-718d-a19b-d176d700a173" xlink:to="loc_ubnt_TermLoanMember_019d1bb6-7090-7722-baf0-6f7c4a158a87" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019d1bb6-7090-7e59-b2c4-a14e772a0531" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-716f-b59c-e33560d21e07" xlink:to="loc_us-gaap_DebtInstrumentAxis_019d1bb6-7090-7e59-b2c4-a14e772a0531" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019d1bb6-7090-7e59-b2c4-a14e772a0531_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019d1bb6-7090-7e59-b2c4-a14e772a0531" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019d1bb6-7090-7e59-b2c4-a14e772a0531_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019d1bb6-7090-7d5f-86dc-5297bb6ec531" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019d1bb6-7090-7e59-b2c4-a14e772a0531" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019d1bb6-7090-7d5f-86dc-5297bb6ec531" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_AmendedAndRestatedCreditAgreementMember_019d1bb6-7090-7ea0-a573-ff83c4624097" xlink:href="ubnt-20260331.xsd#ubnt_AmendedAndRestatedCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019d1bb6-7090-7d5f-86dc-5297bb6ec531" xlink:to="loc_ubnt_AmendedAndRestatedCreditAgreementMember_019d1bb6-7090-7ea0-a573-ff83c4624097" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_TermLoanMember_019d1bb6-7090-70e2-a6ea-70a677ea1e26" xlink:href="ubnt-20260331.xsd#ubnt_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019d1bb6-7090-7d5f-86dc-5297bb6ec531" xlink:to="loc_ubnt_TermLoanMember_019d1bb6-7090-70e2-a6ea-70a677ea1e26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d1bb6-7090-7957-9af3-18a26b477105" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-716f-b59c-e33560d21e07" xlink:to="loc_srt_RangeAxis_019d1bb6-7090-7957-9af3-18a26b477105" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d1bb6-7090-7957-9af3-18a26b477105_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019d1bb6-7090-7957-9af3-18a26b477105" xlink:to="loc_srt_RangeMember_019d1bb6-7090-7957-9af3-18a26b477105_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d1bb6-7090-7776-9ce0-3a6c08abbe90" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019d1bb6-7090-7957-9af3-18a26b477105" xlink:to="loc_srt_RangeMember_019d1bb6-7090-7776-9ce0-3a6c08abbe90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019d1bb6-7090-7a71-bbdc-23adaefb7587" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d1bb6-7090-7776-9ce0-3a6c08abbe90" xlink:to="loc_srt_MinimumMember_019d1bb6-7090-7a71-bbdc-23adaefb7587" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019d1bb6-7090-7cab-8875-c1abb938c6b9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d1bb6-7090-7776-9ce0-3a6c08abbe90" xlink:to="loc_srt_MaximumMember_019d1bb6-7090-7cab-8875-c1abb938c6b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019d1bb6-7090-77fb-bd5b-70c44096a3ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-716f-b59c-e33560d21e07" xlink:to="loc_us-gaap_VariableRateAxis_019d1bb6-7090-77fb-bd5b-70c44096a3ad" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019d1bb6-7090-77fb-bd5b-70c44096a3ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019d1bb6-7090-77fb-bd5b-70c44096a3ad" xlink:to="loc_us-gaap_VariableRateDomain_019d1bb6-7090-77fb-bd5b-70c44096a3ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019d1bb6-7090-768d-85a8-f0b8487790c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019d1bb6-7090-77fb-bd5b-70c44096a3ad" xlink:to="loc_us-gaap_VariableRateDomain_019d1bb6-7090-768d-85a8-f0b8487790c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_019d1bb6-7090-7a30-b672-5307d9a954d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019d1bb6-7090-768d-85a8-f0b8487790c8" xlink:to="loc_us-gaap_BaseRateMember_019d1bb6-7090-7a30-b672-5307d9a954d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019d1bb6-7090-78b1-a55a-7eb17f7a12d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019d1bb6-7090-768d-85a8-f0b8487790c8" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019d1bb6-7090-78b1-a55a-7eb17f7a12d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_019d1bb6-7090-7311-b378-121fe4ab7e69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019d1bb6-7090-768d-85a8-f0b8487790c8" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_019d1bb6-7090-7311-b378-121fe4ab7e69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_SOFROneMonthRateMember_019d1bb6-7090-7eda-b963-b1263ebdf66d" xlink:href="ubnt-20260331.xsd#ubnt_SOFROneMonthRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019d1bb6-7090-768d-85a8-f0b8487790c8" xlink:to="loc_ubnt_SOFROneMonthRateMember_019d1bb6-7090-7eda-b963-b1263ebdf66d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ApplicableInterestRateMember_019d1bb6-7090-7e92-b4b2-b2c03f27c804" xlink:href="ubnt-20260331.xsd#ubnt_ApplicableInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019d1bb6-7090-768d-85a8-f0b8487790c8" xlink:to="loc_ubnt_ApplicableInterestRateMember_019d1bb6-7090-7e92-b4b2-b2c03f27c804" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019df1bc-1222-7239-8310-f5dec8469dff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_LineOfCredit_019df1bc-1222-7239-8310-f5dec8469dff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermLinesOfCredit_019d1bb6-7090-7659-8e58-bb729830461d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfLongTermLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_RepaymentsOfLongTermLinesOfCredit_019d1bb6-7090-7659-8e58-bb729830461d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_RepaymentofLongTermLinesofCreditPrincipal_019d1bb6-7090-7fd8-a257-55013c4e786a" xlink:href="ubnt-20260331.xsd#ubnt_RepaymentofLongTermLinesofCreditPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_ubnt_RepaymentofLongTermLinesofCreditPrincipal_019d1bb6-7090-7fd8-a257-55013c4e786a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_RepaymentofLongTermLinesofCreditInterest_019d1bb6-7090-7ddb-9bed-873a10c009f1" xlink:href="ubnt-20260331.xsd#ubnt_RepaymentofLongTermLinesofCreditInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_ubnt_RepaymentofLongTermLinesofCreditInterest_019d1bb6-7090-7ddb-9bed-873a10c009f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_019df488-2947-72dd-a869-1adad9142284" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_019df488-2947-72dd-a869-1adad9142284" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019d1bb6-7090-70e3-a829-097e2e096e41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019d1bb6-7090-70e3-a829-097e2e096e41" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_LineofCreditFacilityOptionAdditionalMaximumBorrowingCapacity_019d1bb6-7090-7e21-baa2-f89be11c98f5" xlink:href="ubnt-20260331.xsd#ubnt_LineofCreditFacilityOptionAdditionalMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_ubnt_LineofCreditFacilityOptionAdditionalMaximumBorrowingCapacity_019d1bb6-7090-7e21-baa2-f89be11c98f5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPayment_019d1bb6-7090-7c0d-8bb2-1d80b10e9354" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentPeriodicPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPayment_019d1bb6-7090-7c0d-8bb2-1d80b10e9354" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019dbe38-b883-7a47-94c6-007c13f3d85e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019dbe38-b883-7a47-94c6-007c13f3d85e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_019d1bb6-7090-72a3-a7c7-e0fb3f3c9312" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_019d1bb6-7090-72a3-a7c7-e0fb3f3c9312" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019d1bb6-7090-70b2-b600-c416b0c48c42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019d1bb6-7090-70b2-b600-c416b0c48c42" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019d1bb6-7090-78b1-a1dd-4c3a52a9ac05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019d1bb6-7090-78b1-a1dd-4c3a52a9ac05" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_DebtInstrumentDebtDefaultBasisSpreadOverApplicableInterestRate_019d1bb6-7090-7edc-bddb-c8e650ec3900" xlink:href="ubnt-20260331.xsd#ubnt_DebtInstrumentDebtDefaultBasisSpreadOverApplicableInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_ubnt_DebtInstrumentDebtDefaultBasisSpreadOverApplicableInterestRate_019d1bb6-7090-7edc-bddb-c8e650ec3900" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019d1bb6-7090-7986-b9f3-eb4a99b4383e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019d1bb6-7090-7986-b9f3-eb4a99b4383e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_LineofCreditFacilityDebtIssuanceCostsPercentageAnnually_019d1bb6-7090-7793-9feb-daff10f9b463" xlink:href="ubnt-20260331.xsd#ubnt_LineofCreditFacilityDebtIssuanceCostsPercentageAnnually"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_ubnt_LineofCreditFacilityDebtIssuanceCostsPercentageAnnually_019d1bb6-7090-7793-9feb-daff10f9b463" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RatioOfIndebtednessToNetCapital1_019d1bb6-7090-7069-9fe6-d9899b1a228f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RatioOfIndebtednessToNetCapital1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_us-gaap_RatioOfIndebtednessToNetCapital1_019d1bb6-7090-7069-9fe6-d9899b1a228f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_LineOfCreditFacilityCovenantTermsCoverageRatio_019d1bb6-7090-7d52-b051-744e0f40b5c3" xlink:href="ubnt-20260331.xsd#ubnt_LineOfCreditFacilityCovenantTermsCoverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-778b-bc8a-2a06dbbbd857" xlink:to="loc_ubnt_LineOfCreditFacilityCovenantTermsCoverageRatio_019d1bb6-7090-7d52-b051-744e0f40b5c3" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/DEBTScheduleofDebtDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#DEBTScheduleofDebtDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/DEBTScheduleofDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-7d87-8687-e08e73c1783a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-7028-962b-b184bf430a7b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-7d87-8687-e08e73c1783a" xlink:to="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-7028-962b-b184bf430a7b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-74d7-b4b4-94c388932b8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019d1bb6-7090-7028-962b-b184bf430a7b" xlink:to="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-74d7-b4b4-94c388932b8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-74d7-b4b4-94c388932b8a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-74d7-b4b4-94c388932b8a" xlink:to="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-74d7-b4b4-94c388932b8a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7b88-b5a3-956fd6fbce8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019d1bb6-7090-74d7-b4b4-94c388932b8a" xlink:to="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7b88-b5a3-956fd6fbce8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_InitialTermLoanMember_019d1bb6-7090-7037-b81b-d73a9909af15" xlink:href="ubnt-20260331.xsd#ubnt_InitialTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d1bb6-7090-7b88-b5a3-956fd6fbce8c" xlink:to="loc_ubnt_InitialTermLoanMember_019d1bb6-7090-7037-b81b-d73a9909af15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ShortTermDebtGross_019d1bb6-7090-7e38-a3f6-5343b78b1cd9" xlink:href="ubnt-20260331.xsd#ubnt_ShortTermDebtGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-7d87-8687-e08e73c1783a" xlink:to="loc_ubnt_ShortTermDebtGross_019d1bb6-7090-7e38-a3f6-5343b78b1cd9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsCurrentNet_019d1bb6-7090-77d7-9ebb-23294fb46095" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsCurrentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-7d87-8687-e08e73c1783a" xlink:to="loc_us-gaap_DeferredFinanceCostsCurrentNet_019d1bb6-7090-77d7-9ebb-23294fb46095" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_019d1bb6-7090-7f71-b97e-93d46cfffcc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d1bb6-7090-7d87-8687-e08e73c1783a" xlink:to="loc_us-gaap_ShortTermBorrowings_019d1bb6-7090-7f71-b97e-93d46cfffcc5" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/LEASESNarrativeDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#LEASESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/LEASESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019d1bb6-714a-7376-856a-540a67e881e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019d1bb6-714a-7554-9dbf-6f051858a12b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019d1bb6-714a-7376-856a-540a67e881e1" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019d1bb6-714a-7554-9dbf-6f051858a12b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d1bb6-714a-7916-aa0a-82f3fad65d8d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019d1bb6-714a-7554-9dbf-6f051858a12b" xlink:to="loc_srt_RangeAxis_019d1bb6-714a-7916-aa0a-82f3fad65d8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d1bb6-714a-7916-aa0a-82f3fad65d8d_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019d1bb6-714a-7916-aa0a-82f3fad65d8d" xlink:to="loc_srt_RangeMember_019d1bb6-714a-7916-aa0a-82f3fad65d8d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d1bb6-714a-72d4-8fa2-8692949fa8ff" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019d1bb6-714a-7916-aa0a-82f3fad65d8d" xlink:to="loc_srt_RangeMember_019d1bb6-714a-72d4-8fa2-8692949fa8ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019d1bb6-714a-7495-a506-193f0f4b0d8a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d1bb6-714a-72d4-8fa2-8692949fa8ff" xlink:to="loc_srt_MinimumMember_019d1bb6-714a-7495-a506-193f0f4b0d8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019d1bb6-714a-73de-9550-bd67429c3414" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d1bb6-714a-72d4-8fa2-8692949fa8ff" xlink:to="loc_srt_MaximumMember_019d1bb6-714a-73de-9550-bd67429c3414" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_019d1bb6-714a-731e-a837-966236792692" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019d1bb6-714a-7376-856a-540a67e881e1" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_019d1bb6-714a-731e-a837-966236792692" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments_019d1bb6-714a-7141-bdea-6a2ecb0bc42a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019d1bb6-714a-7376-856a-540a67e881e1" xlink:to="loc_us-gaap_OperatingLeasePayments_019d1bb6-714a-7141-bdea-6a2ecb0bc42a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/LEASESScheduleofLeaseCostsDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#LEASESScheduleofLeaseCostsDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/LEASESScheduleofLeaseCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019d1bb6-714a-7b48-9e71-4aab24049e2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019d1bb6-714a-7b7f-8914-cb390a033ae8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019d1bb6-714a-7b48-9e71-4aab24049e2c" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019d1bb6-714a-7b7f-8914-cb390a033ae8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019d1bb6-714a-743d-87d2-804c6b27a89d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019d1bb6-714a-7b7f-8914-cb390a033ae8" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019d1bb6-714a-743d-87d2-804c6b27a89d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-743d-87d2-804c6b27a89d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019d1bb6-714a-743d-87d2-804c6b27a89d" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-743d-87d2-804c6b27a89d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7b6a-8290-2fc4f499aede" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019d1bb6-714a-743d-87d2-804c6b27a89d" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7b6a-8290-2fc4f499aede" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenseMember_019d1bb6-714a-7f9f-ba1f-8c922f34d2ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7b6a-8290-2fc4f499aede" xlink:to="loc_us-gaap_OperatingExpenseMember_019d1bb6-714a-7f9f-ba1f-8c922f34d2ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_019d1bb6-714a-7d23-a543-f963007e2944" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7b6a-8290-2fc4f499aede" xlink:to="loc_us-gaap_CostOfSalesMember_019d1bb6-714a-7d23-a543-f963007e2944" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseCostAbstract_019d1bb6-714a-7f7a-89c8-df01ce79fabe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019d1bb6-714a-7b48-9e71-4aab24049e2c" xlink:to="loc_us-gaap_LeaseCostAbstract_019d1bb6-714a-7f7a-89c8-df01ce79fabe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseCost_019d1bb6-714a-7d59-93a1-9aad53980280" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseCostAbstract_019d1bb6-714a-7f7a-89c8-df01ce79fabe" xlink:to="loc_us-gaap_OperatingLeaseCost_019d1bb6-714a-7d59-93a1-9aad53980280" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableLeaseCost_019d1bb6-714a-7d92-9bb4-27b9031e73ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseCostAbstract_019d1bb6-714a-7f7a-89c8-df01ce79fabe" xlink:to="loc_us-gaap_VariableLeaseCost_019d1bb6-714a-7d92-9bb4-27b9031e73ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseCost_019d1bb6-714a-7552-8271-17a234b78a0c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseCostAbstract_019d1bb6-714a-7f7a-89c8-df01ce79fabe" xlink:to="loc_us-gaap_LeaseCost_019d1bb6-714a-7552-8271-17a234b78a0c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/SHAREBASEDCOMPENSATIONNarrativeDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#SHAREBASEDCOMPENSATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/SHAREBASEDCOMPENSATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-714a-7069-8e22-a68fbcbd34b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-714a-7069-8e22-a68fbcbd34b9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019d1bb6-714a-7014-8784-d23149a856bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-714a-7069-8e22-a68fbcbd34b9" xlink:to="loc_us-gaap_AwardTypeAxis_019d1bb6-714a-7014-8784-d23149a856bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7014-8784-d23149a856bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019d1bb6-714a-7014-8784-d23149a856bd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7014-8784-d23149a856bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7151-96d4-9be28d13b134" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019d1bb6-714a-7014-8784-d23149a856bd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7151-96d4-9be28d13b134" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019d1bb6-714a-7b93-9d72-986d576d4136" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7151-96d4-9be28d13b134" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019d1bb6-714a-7b93-9d72-986d576d4136" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019d1bb6-714a-77ae-8fbb-ac4abd8fad14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7151-96d4-9be28d13b134" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019d1bb6-714a-77ae-8fbb-ac4abd8fad14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019d1bb6-714a-79c4-b877-5dd5dcbf940a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019d1bb6-714a-79c4-b877-5dd5dcbf940a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019d1bb6-714a-747f-a116-346633ed6a9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019d1bb6-714a-747f-a116-346633ed6a9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019d1bb6-714a-7d0d-866a-0ae339b25fd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019d1bb6-714a-7d0d-866a-0ae339b25fd3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019d1bb6-714a-7c9d-b142-4a915bd0c244" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019d1bb6-714a-7c9d-b142-4a915bd0c244" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionVestedInPeriodIntrinsicValue_019d1bb6-714a-7c34-a01d-11805b7a3c10" xlink:href="ubnt-20260331.xsd#ubnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionVestedInPeriodIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:to="loc_ubnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionVestedInPeriodIntrinsicValue_019d1bb6-714a-7c34-a01d-11805b7a3c10" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionNonvestedIntrinsicValue_019d1bb6-714a-7c9f-a62a-2f15219b86c6" xlink:href="ubnt-20260331.xsd#ubnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionNonvestedIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:to="loc_ubnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionNonvestedIntrinsicValue_019d1bb6-714a-7c9f-a62a-2f15219b86c6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019d1bb6-714a-7b2c-b613-c6e89c7ce698" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7ab8-a396-a802d8bbee2a" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019d1bb6-714a-7b2c-b613-c6e89c7ce698" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019d1bb6-714a-7024-a039-1d995fa412b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019d1bb6-714a-7b7a-82b9-693089a1a8ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019d1bb6-714a-7024-a039-1d995fa412b2" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019d1bb6-714a-7b7a-82b9-693089a1a8ee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019d1bb6-714a-7231-b3fa-344f9e19c559" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019d1bb6-714a-7b7a-82b9-693089a1a8ee" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019d1bb6-714a-7231-b3fa-344f9e19c559" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7231-b3fa-344f9e19c559_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019d1bb6-714a-7231-b3fa-344f9e19c559" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7231-b3fa-344f9e19c559_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7135-ac71-0518ee11c923" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019d1bb6-714a-7231-b3fa-344f9e19c559" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7135-ac71-0518ee11c923" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_019d1bb6-714a-78bc-95d9-321c289b6486" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7135-ac71-0518ee11c923" xlink:to="loc_us-gaap_CostOfSalesMember_019d1bb6-714a-78bc-95d9-321c289b6486" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019d1bb6-714a-701e-b2c4-e11a636eef9d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7135-ac71-0518ee11c923" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019d1bb6-714a-701e-b2c4-e11a636eef9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_019d1bb6-714a-7d73-966d-61e3c5b0afe3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019d1bb6-714a-7135-ac71-0518ee11c923" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_019d1bb6-714a-7d73-966d-61e3c5b0afe3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019d1bb6-714a-790c-9dec-089837f1bb7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019d1bb6-714a-7024-a039-1d995fa412b2" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019d1bb6-714a-790c-9dec-089837f1bb7d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/SHAREBASEDCOMPENSATIONScheduleofRSUActivityDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#SHAREBASEDCOMPENSATIONScheduleofRSUActivityDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/SHAREBASEDCOMPENSATIONScheduleofRSUActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7da9-bfd6-b4716ca56392" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-714a-7a18-93f3-c9e9a9515dbe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7da9-bfd6-b4716ca56392" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-714a-7a18-93f3-c9e9a9515dbe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019d1bb6-714a-773c-a32c-9a91243aa270" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019d1bb6-714a-7a18-93f3-c9e9a9515dbe" xlink:to="loc_us-gaap_AwardTypeAxis_019d1bb6-714a-773c-a32c-9a91243aa270" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-773c-a32c-9a91243aa270_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019d1bb6-714a-773c-a32c-9a91243aa270" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-773c-a32c-9a91243aa270_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7dfa-ad4d-9a6659d46af1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019d1bb6-714a-773c-a32c-9a91243aa270" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7dfa-ad4d-9a6659d46af1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019d1bb6-714a-73dc-8bce-21880915ab3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d1bb6-714a-7dfa-ad4d-9a6659d46af1" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019d1bb6-714a-73dc-8bce-21880915ab3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019d1bb6-714a-71b4-9d99-f63d9bc4a197" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7da9-bfd6-b4716ca56392" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019d1bb6-714a-71b4-9d99-f63d9bc4a197" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019d1bb6-714a-75e7-b0ba-f00732413f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019d1bb6-714a-71b4-9d99-f63d9bc4a197" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019d1bb6-714a-75e7-b0ba-f00732413f5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019d1bb6-714a-7e89-97f7-a88420e96e94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019d1bb6-714a-71b4-9d99-f63d9bc4a197" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019d1bb6-714a-7e89-97f7-a88420e96e94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019d1bb6-714a-768f-8c47-d3185366c174" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019d1bb6-714a-71b4-9d99-f63d9bc4a197" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019d1bb6-714a-768f-8c47-d3185366c174" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019d1bb6-714a-7db7-8bab-61ca9adb392b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019d1bb6-714a-71b4-9d99-f63d9bc4a197" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019d1bb6-714a-7db7-8bab-61ca9adb392b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019d1bb6-714a-77bd-b787-4e7f78289950" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019d1bb6-714a-77dd-bce2-50b950239177" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019d1bb6-714a-7da9-bfd6-b4716ca56392" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019d1bb6-714a-77dd-bce2-50b950239177" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019d1bb6-714a-7c73-a60a-cc2b76083e44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019d1bb6-714a-77dd-bce2-50b950239177" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019d1bb6-714a-7c73-a60a-cc2b76083e44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019d1bb6-714a-7ced-b947-983703ba7039" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019d1bb6-714a-77dd-bce2-50b950239177" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019d1bb6-714a-7ced-b947-983703ba7039" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019d1bb6-714a-74df-b02a-79eac0d0cbce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019d1bb6-714a-77dd-bce2-50b950239177" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019d1bb6-714a-74df-b02a-79eac0d0cbce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019d1bb6-714a-7ff8-8c88-4cd0bf25ccf9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019d1bb6-714a-77dd-bce2-50b950239177" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019d1bb6-714a-7ff8-8c88-4cd0bf25ccf9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019d1bb6-714a-7b2b-939c-07258f544a27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/INCOMETAXESDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#INCOMETAXESDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/INCOMETAXESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_019d1bb6-714a-7cc6-9259-21e718acfe62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable_019d1bb6-714a-7b10-a02c-66be4c1b37c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_019d1bb6-714a-7cc6-9259-21e718acfe62" xlink:to="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable_019d1bb6-714a-7b10-a02c-66be4c1b37c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019d1bb6-714a-7315-a680-0323a0a7de1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable_019d1bb6-714a-7b10-a02c-66be4c1b37c0" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019d1bb6-714a-7315-a680-0323a0a7de1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019d1bb6-714a-7315-a680-0323a0a7de1d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019d1bb6-714a-7315-a680-0323a0a7de1d" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019d1bb6-714a-7315-a680-0323a0a7de1d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019d1bb6-714a-7cd2-85d9-caff89cda0a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019d1bb6-714a-7315-a680-0323a0a7de1d" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019d1bb6-714a-7cd2-85d9-caff89cda0a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalRevenueServiceIRSMember_019d1bb6-714a-7104-b3a3-13f7b2943d47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InternalRevenueServiceIRSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019d1bb6-714a-7cd2-85d9-caff89cda0a0" xlink:to="loc_us-gaap_InternalRevenueServiceIRSMember_019d1bb6-714a-7104-b3a3-13f7b2943d47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameAxis_019d1bb6-714a-77a8-9751-cd7521e4392b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable_019d1bb6-714a-7b10-a02c-66be4c1b37c0" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameAxis_019d1bb6-714a-77a8-9751-cd7521e4392b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameDomain_019d1bb6-714a-77a8-9751-cd7521e4392b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameAxis_019d1bb6-714a-77a8-9751-cd7521e4392b" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameDomain_019d1bb6-714a-77a8-9751-cd7521e4392b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameDomain_019d1bb6-714a-796c-bb7d-66f774f93af9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameAxis_019d1bb6-714a-77a8-9751-cd7521e4392b" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameDomain_019d1bb6-714a-796c-bb7d-66f774f93af9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InlandRevenueHongKongMember_019d1bb6-714a-7380-a95c-62687718718e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InlandRevenueHongKongMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameDomain_019d1bb6-714a-796c-bb7d-66f774f93af9" xlink:to="loc_us-gaap_InlandRevenueHongKongMember_019d1bb6-714a-7380-a95c-62687718718e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodAxis_019d1bb6-714a-7e2f-9a9b-86dd444e28fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable_019d1bb6-714a-7b10-a02c-66be4c1b37c0" xlink:to="loc_us-gaap_TaxPeriodAxis_019d1bb6-714a-7e2f-9a9b-86dd444e28fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_019d1bb6-714a-7e2f-9a9b-86dd444e28fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxPeriodAxis_019d1bb6-714a-7e2f-9a9b-86dd444e28fa" xlink:to="loc_us-gaap_TaxPeriodDomain_019d1bb6-714a-7e2f-9a9b-86dd444e28fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_019d1bb6-714a-7d0c-981a-290f4d51f237" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxPeriodAxis_019d1bb6-714a-7e2f-9a9b-86dd444e28fa" xlink:to="loc_us-gaap_TaxPeriodDomain_019d1bb6-714a-7d0c-981a-290f4d51f237" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_TaxYear20102019Member_019d1bb6-714a-776d-82a5-771785cb9918" xlink:href="ubnt-20260331.xsd#ubnt_TaxYear20102019Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_019d1bb6-714a-7d0c-981a-290f4d51f237" xlink:to="loc_ubnt_TaxYear20102019Member_019d1bb6-714a-776d-82a5-771785cb9918" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxYear2020Member_019dd45b-70fd-72a5-b37d-6f2ba9dd1b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxYear2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_019d1bb6-714a-7d0c-981a-290f4d51f237" xlink:to="loc_us-gaap_TaxYear2020Member_019dd45b-70fd-72a5-b37d-6f2ba9dd1b1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_019d1bb6-714a-7888-8ebe-eab2215eced9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_019d1bb6-714a-7cc6-9259-21e718acfe62" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_019d1bb6-714a-7888-8ebe-eab2215eced9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_PaymentForTaxDeposit_019d1bb6-714a-7abf-a07d-c8132c4bfa8d" xlink:href="ubnt-20260331.xsd#ubnt_PaymentForTaxDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_019d1bb6-714a-7cc6-9259-21e718acfe62" xlink:to="loc_ubnt_PaymentForTaxDeposit_019d1bb6-714a-7abf-a07d-c8132c4bfa8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_AdditionalTaxDepositRequested_019d1bb6-714a-76bb-973f-af2e958e34bc" xlink:href="ubnt-20260331.xsd#ubnt_AdditionalTaxDepositRequested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_019d1bb6-714a-7cc6-9259-21e718acfe62" xlink:to="loc_ubnt_AdditionalTaxDepositRequested_019d1bb6-714a-76bb-973f-af2e958e34bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_EstimatedGlobalMinimumTaxExpense_019d1bb6-714a-799c-bd45-6c8274743a49" xlink:href="ubnt-20260331.xsd#ubnt_EstimatedGlobalMinimumTaxExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_019d1bb6-714a-7cc6-9259-21e718acfe62" xlink:to="loc_ubnt_EstimatedGlobalMinimumTaxExpense_019d1bb6-714a-799c-bd45-6c8274743a49" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofRevenuesbyProductDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofRevenuesbyProductDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofRevenuesbyProductDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019d1bb6-714a-724d-a67e-4c533f27fb69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-7961-9efd-7dce1bd19256" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d1bb6-714a-724d-a67e-4c533f27fb69" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-7961-9efd-7dce1bd19256" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019d1bb6-714a-71a1-ac6d-577ffc9ffa93" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-7961-9efd-7dce1bd19256" xlink:to="loc_srt_ProductOrServiceAxis_019d1bb6-714a-71a1-ac6d-577ffc9ffa93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d1bb6-714a-71a1-ac6d-577ffc9ffa93_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019d1bb6-714a-71a1-ac6d-577ffc9ffa93" xlink:to="loc_srt_ProductsAndServicesDomain_019d1bb6-714a-71a1-ac6d-577ffc9ffa93_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019d1bb6-714a-7abd-8455-07d528b54de1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019d1bb6-714a-71a1-ac6d-577ffc9ffa93" xlink:to="loc_srt_ProductsAndServicesDomain_019d1bb6-714a-7abd-8455-07d528b54de1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_EnterpriseTechnologyMember_019d1bb6-714a-7d60-a5a1-3ad063d852d1" xlink:href="ubnt-20260331.xsd#ubnt_EnterpriseTechnologyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d1bb6-714a-7abd-8455-07d528b54de1" xlink:to="loc_ubnt_EnterpriseTechnologyMember_019d1bb6-714a-7d60-a5a1-3ad063d852d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ServiceProviderTechnologyMember_019d1bb6-714a-7f81-a315-4e56b0008d83" xlink:href="ubnt-20260331.xsd#ubnt_ServiceProviderTechnologyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019d1bb6-714a-7abd-8455-07d528b54de1" xlink:to="loc_ubnt_ServiceProviderTechnologyMember_019d1bb6-714a-7f81-a315-4e56b0008d83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-75ac-8e60-68af49a00dd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-7961-9efd-7dce1bd19256" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-75ac-8e60-68af49a00dd5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-75ac-8e60-68af49a00dd5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-75ac-8e60-68af49a00dd5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-75ac-8e60-68af49a00dd5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-719b-b33e-b22ae0472005" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-75ac-8e60-68af49a00dd5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-719b-b33e-b22ae0472005" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_019d1bb6-714a-7ea6-a983-5546d1d56ba1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-719b-b33e-b22ae0472005" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_019d1bb6-714a-7ea6-a983-5546d1d56ba1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-72ed-ad97-e9fc5dadb928" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-7961-9efd-7dce1bd19256" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-72ed-ad97-e9fc5dadb928" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-72ed-ad97-e9fc5dadb928_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-72ed-ad97-e9fc5dadb928" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-72ed-ad97-e9fc5dadb928_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-764e-b79d-8d813191c854" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-72ed-ad97-e9fc5dadb928" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-764e-b79d-8d813191c854" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019d1bb6-714a-7f58-ba02-dda2482a555d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-764e-b79d-8d813191c854" xlink:to="loc_us-gaap_SalesRevenueNetMember_019d1bb6-714a-7f58-ba02-dda2482a555d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019d1bb6-714a-7fc8-8c70-b46479cbb7e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d1bb6-714a-724d-a67e-4c533f27fb69" xlink:to="loc_us-gaap_Revenues_019d1bb6-714a-7fc8-8c70-b46479cbb7e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019d1bb6-714a-71f6-b8c2-ecbacaa529ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d1bb6-714a-724d-a67e-4c533f27fb69" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019d1bb6-714a-71f6-b8c2-ecbacaa529ef" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofRevenuesbyGeographyDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofRevenuesbyGeographyDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofRevenuesbyGeographyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019d1bb6-714a-7c82-bb9f-cec367459f80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-75ea-a039-00b8ee7de344" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d1bb6-714a-7c82-bb9f-cec367459f80" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-75ea-a039-00b8ee7de344" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-7028-be5f-e92298697ccc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-75ea-a039-00b8ee7de344" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-7028-be5f-e92298697ccc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-7028-be5f-e92298697ccc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-7028-be5f-e92298697ccc" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-7028-be5f-e92298697ccc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-702b-b183-46fc9e1cd774" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-7028-be5f-e92298697ccc" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-702b-b183-46fc9e1cd774" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019d1bb6-714a-7f9c-aa20-621010d78923" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-702b-b183-46fc9e1cd774" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019d1bb6-714a-7f9c-aa20-621010d78923" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-7113-8f2c-db7a7ce351ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-75ea-a039-00b8ee7de344" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-7113-8f2c-db7a7ce351ac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-7113-8f2c-db7a7ce351ac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-7113-8f2c-db7a7ce351ac" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-7113-8f2c-db7a7ce351ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-729c-b51c-650f0c64bc66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-7113-8f2c-db7a7ce351ac" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-729c-b51c-650f0c64bc66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019d1bb6-714a-7e8f-88f2-25270ed11115" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-729c-b51c-650f0c64bc66" xlink:to="loc_us-gaap_SalesRevenueNetMember_019d1bb6-714a-7e8f-88f2-25270ed11115" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019d1bb6-714a-7848-9650-4f73ecb20a80" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d1bb6-714a-75ea-a039-00b8ee7de344" xlink:to="loc_srt_StatementGeographicalAxis_019d1bb6-714a-7848-9650-4f73ecb20a80" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-7848-9650-4f73ecb20a80_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019d1bb6-714a-7848-9650-4f73ecb20a80" xlink:to="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-7848-9650-4f73ecb20a80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-75b0-9a44-96ac22810646" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019d1bb6-714a-7848-9650-4f73ecb20a80" xlink:to="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-75b0-9a44-96ac22810646" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NorthAmericaMember_019d1bb6-714a-7c71-bcb9-55080a780ba7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NorthAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-75b0-9a44-96ac22810646" xlink:to="loc_srt_NorthAmericaMember_019d1bb6-714a-7c71-bcb9-55080a780ba7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_019d1bb6-714a-7075-a897-7750dce00517" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-75b0-9a44-96ac22810646" xlink:to="loc_us-gaap_EMEAMember_019d1bb6-714a-7075-a897-7750dce00517" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_019d1bb6-714a-716f-9ee3-71fdedb8c220" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-75b0-9a44-96ac22810646" xlink:to="loc_srt_AsiaPacificMember_019d1bb6-714a-716f-9ee3-71fdedb8c220" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SouthAmericaMember_019d1bb6-714a-7671-9c61-a655a3d95e5f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SouthAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-75b0-9a44-96ac22810646" xlink:to="loc_srt_SouthAmericaMember_019d1bb6-714a-7671-9c61-a655a3d95e5f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019d1bb6-714a-725b-acd5-41a20de9edb1" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019d1bb6-714a-75b0-9a44-96ac22810646" xlink:to="loc_country_US_019d1bb6-714a-725b-acd5-41a20de9edb1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019d1bb6-714a-7f54-b947-b507d31499e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d1bb6-714a-7c82-bb9f-cec367459f80" xlink:to="loc_us-gaap_Revenues_019d1bb6-714a-7f54-b947-b507d31499e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019d1bb6-714a-7c9f-973a-5dce5158bc27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019d1bb6-714a-7c82-bb9f-cec367459f80" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019d1bb6-714a-7c9f-973a-5dce5158bc27" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofConcentrationofRiskbyCustomerDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofConcentrationofRiskbyCustomerDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/SEGMENTINFORMATIONREVENUESBYGEOGRAPHYANDSIGNIFICANTCUSTOMERSScheduleofConcentrationofRiskbyCustomerDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019d1bb6-714a-7358-8c50-68194ff2bf01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EntityWideRevenueMajorCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019d1bb6-714a-7e62-9ddc-7d977ca8df3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019d1bb6-714a-7358-8c50-68194ff2bf01" xlink:to="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019d1bb6-714a-7e62-9ddc-7d977ca8df3d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-78bd-a438-212c0f4228b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019d1bb6-714a-7e62-9ddc-7d977ca8df3d" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-78bd-a438-212c0f4228b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-78bd-a438-212c0f4228b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-78bd-a438-212c0f4228b8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-78bd-a438-212c0f4228b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-70fd-a70d-81e4fbf55895" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1bb6-714a-78bd-a438-212c0f4228b8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-70fd-a70d-81e4fbf55895" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019d1bb6-714a-71a5-b5f9-beb1b99913db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019d1bb6-714a-70fd-a70d-81e4fbf55895" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019d1bb6-714a-71a5-b5f9-beb1b99913db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-7e1e-bdb2-fd84fd1309cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019d1bb6-714a-7e62-9ddc-7d977ca8df3d" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-7e1e-bdb2-fd84fd1309cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-7e1e-bdb2-fd84fd1309cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-7e1e-bdb2-fd84fd1309cd" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-7e1e-bdb2-fd84fd1309cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-7a62-983b-672785e42a84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1bb6-714a-7e1e-bdb2-fd84fd1309cd" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-7a62-983b-672785e42a84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019d1bb6-714a-79bc-8bb5-ef2e0393db81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1bb6-714a-7a62-983b-672785e42a84" xlink:to="loc_us-gaap_AccountsReceivableMember_019d1bb6-714a-79bc-8bb5-ef2e0393db81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019d1bb6-714a-710f-ad97-0c15906b21ef" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019d1bb6-714a-7e62-9ddc-7d977ca8df3d" xlink:to="loc_srt_MajorCustomersAxis_019d1bb6-714a-710f-ad97-0c15906b21ef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019d1bb6-714a-710f-ad97-0c15906b21ef_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019d1bb6-714a-710f-ad97-0c15906b21ef" xlink:to="loc_srt_NameOfMajorCustomerDomain_019d1bb6-714a-710f-ad97-0c15906b21ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019d1bb6-714a-7357-bc34-f3b32a9b3e2b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019d1bb6-714a-710f-ad97-0c15906b21ef" xlink:to="loc_srt_NameOfMajorCustomerDomain_019d1bb6-714a-7357-bc34-f3b32a9b3e2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_CustomerAMember_019d1bb6-714a-7ac2-b70b-65954f1ea57d" xlink:href="ubnt-20260331.xsd#ubnt_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019d1bb6-714a-7357-bc34-f3b32a9b3e2b" xlink:to="loc_ubnt_CustomerAMember_019d1bb6-714a-7ac2-b70b-65954f1ea57d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019d1bb6-714a-716e-891a-7344da57d50b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019d1bb6-714a-7358-8c50-68194ff2bf01" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019d1bb6-714a-716e-891a-7344da57d50b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/COMMONSTOCKANDTREASURYSTOCKDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#COMMONSTOCKANDTREASURYSTOCKDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/COMMONSTOCKANDTREASURYSTOCKDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d1bb6-714a-797c-b527-4a53be24fecf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityClassOfTreasuryStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfTreasuryStockTable_019d1bb6-714a-73e2-948d-a2064d5354c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfTreasuryStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d1bb6-714a-797c-b527-4a53be24fecf" xlink:to="loc_us-gaap_ClassOfTreasuryStockTable_019d1bb6-714a-73e2-948d-a2064d5354c9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_019d1bb6-714a-7ff4-9338-472df6cd8c9e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfTreasuryStockTable_019d1bb6-714a-73e2-948d-a2064d5354c9" xlink:to="loc_srt_ShareRepurchaseProgramAxis_019d1bb6-714a-7ff4-9338-472df6cd8c9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019d1bb6-714a-7ff4-9338-472df6cd8c9e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019d1bb6-714a-7ff4-9338-472df6cd8c9e" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019d1bb6-714a-7ff4-9338-472df6cd8c9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019d1bb6-714a-7e08-8fee-00c68baa095d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019d1bb6-714a-7ff4-9338-472df6cd8c9e" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019d1bb6-714a-7e08-8fee-00c68baa095d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_A2025AugustProgramMember_019d1bb6-714a-76f1-acc9-87923b5252d3" xlink:href="ubnt-20260331.xsd#ubnt_A2025AugustProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019d1bb6-714a-7e08-8fee-00c68baa095d" xlink:to="loc_ubnt_A2025AugustProgramMember_019d1bb6-714a-76f1-acc9-87923b5252d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019d1bb6-714a-7296-ac72-c9d77d621c18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfTreasuryStockTable_019d1bb6-714a-73e2-948d-a2064d5354c9" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019d1bb6-714a-7296-ac72-c9d77d621c18" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d1bb6-714a-7296-ac72-c9d77d621c18_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d1bb6-714a-7296-ac72-c9d77d621c18" xlink:to="loc_us-gaap_EquityComponentDomain_019d1bb6-714a-7296-ac72-c9d77d621c18_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d1bb6-714a-7d99-9e4e-f3800d38aafd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d1bb6-714a-7296-ac72-c9d77d621c18" xlink:to="loc_us-gaap_EquityComponentDomain_019d1bb6-714a-7d99-9e4e-f3800d38aafd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019d1bb6-714a-7885-873f-b2e2558f6d9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d1bb6-714a-7d99-9e4e-f3800d38aafd" xlink:to="loc_us-gaap_CommonStockMember_019d1bb6-714a-7885-873f-b2e2558f6d9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019d1bb6-714a-7fd7-ab06-699cd293bdd1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019d1bb6-714a-797c-b527-4a53be24fecf" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019d1bb6-714a-7fd7-ab06-699cd293bdd1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/RELATEDPARTYTRANSACTIONSANDCERTAINOTHERTRANSACTIONSDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#RELATEDPARTYTRANSACTIONSANDCERTAINOTHERTRANSACTIONSDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/RELATEDPARTYTRANSACTIONSANDCERTAINOTHERTRANSACTIONSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019d1bb6-714a-7252-a6e0-7e65caccc0cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019d1bb6-714a-7825-ad80-0243f4000b92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019d1bb6-714a-7252-a6e0-7e65caccc0cd" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019d1bb6-714a-7825-ad80-0243f4000b92" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019d1bb6-714a-7dc7-a3b7-652b026fa3ca" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019d1bb6-714a-7825-ad80-0243f4000b92" xlink:to="loc_srt_TitleOfIndividualAxis_019d1bb6-714a-7dc7-a3b7-652b026fa3ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019d1bb6-714a-7dc7-a3b7-652b026fa3ca_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019d1bb6-714a-7dc7-a3b7-652b026fa3ca" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019d1bb6-714a-7dc7-a3b7-652b026fa3ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019d1bb6-714a-732e-8d59-b98ce2649af5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019d1bb6-714a-7dc7-a3b7-652b026fa3ca" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019d1bb6-714a-732e-8d59-b98ce2649af5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ChiefExecutiveOfficerMember_019d1bb6-714a-7f98-8a46-74a2b8642884" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019d1bb6-714a-732e-8d59-b98ce2649af5" xlink:to="loc_srt_ChiefExecutiveOfficerMember_019d1bb6-714a-7f98-8a46-74a2b8642884" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019d1bb6-714a-7aa0-81ad-91dfb7c46060" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019d1bb6-714a-7825-ad80-0243f4000b92" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019d1bb6-714a-7aa0-81ad-91dfb7c46060" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019d1bb6-714a-7aa0-81ad-91dfb7c46060_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019d1bb6-714a-7aa0-81ad-91dfb7c46060" xlink:to="loc_us-gaap_RelatedPartyDomain_019d1bb6-714a-7aa0-81ad-91dfb7c46060_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019d1bb6-714a-7651-931b-c6fa748b5a23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019d1bb6-714a-7aa0-81ad-91dfb7c46060" xlink:to="loc_us-gaap_RelatedPartyDomain_019d1bb6-714a-7651-931b-c6fa748b5a23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019d1bb6-714a-703a-bfbf-7fc3451c3a89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019d1bb6-714a-7651-931b-c6fa748b5a23" xlink:to="loc_us-gaap_RelatedPartyMember_019d1bb6-714a-703a-bfbf-7fc3451c3a89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019d1bb6-714a-766e-9dd3-e8fecd0ac23e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019d1bb6-714a-7252-a6e0-7e65caccc0cd" xlink:to="loc_us-gaap_Revenues_019d1bb6-714a-766e-9dd3-e8fecd0ac23e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ui.com/role/SUBSEQUENTEVENTSDetails" xlink:type="simple" xlink:href="ubnt-20260331.xsd#SUBSEQUENTEVENTSDetails"/>
  <link:definitionLink xlink:role="http://www.ui.com/role/SUBSEQUENTEVENTSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019dbda1-e465-760d-8535-5e49573ec91b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_us-gaap_SubsequentEventTable_019dbda1-e465-760d-8535-5e49573ec91b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019dbda1-e465-75d5-a7ba-f5126e788dcf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019dbda1-e465-760d-8535-5e49573ec91b" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019dbda1-e465-75d5-a7ba-f5126e788dcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dbda1-e465-75d5-a7ba-f5126e788dcf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dbda1-e465-75d5-a7ba-f5126e788dcf" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dbda1-e465-75d5-a7ba-f5126e788dcf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dbda1-e465-7d97-b6aa-b3455339b1f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dbda1-e465-75d5-a7ba-f5126e788dcf" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dbda1-e465-7d97-b6aa-b3455339b1f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019dbda1-e465-72de-bcde-babb20a34fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019dbda1-e465-7d97-b6aa-b3455339b1f6" xlink:to="loc_us-gaap_SubsequentEventMember_019dbda1-e465-72de-bcde-babb20a34fa5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019e041e-51f8-7741-abf6-f320dae0c9da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019dbda1-e465-760d-8535-5e49573ec91b" xlink:to="loc_us-gaap_CreditFacilityAxis_019e041e-51f8-7741-abf6-f320dae0c9da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e041e-51f8-7741-abf6-f320dae0c9da_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019e041e-51f8-7741-abf6-f320dae0c9da" xlink:to="loc_us-gaap_CreditFacilityDomain_019e041e-51f8-7741-abf6-f320dae0c9da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e041e-7772-7f59-9173-ee7d1439c622" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019e041e-51f8-7741-abf6-f320dae0c9da" xlink:to="loc_us-gaap_CreditFacilityDomain_019e041e-7772-7f59-9173-ee7d1439c622" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019e041e-c0f6-775d-a39f-755aace59597" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019e041e-7772-7f59-9173-ee7d1439c622" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019e041e-c0f6-775d-a39f-755aace59597" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_019e0425-bb61-7fbe-8e6b-709292888f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019e041e-7772-7f59-9173-ee7d1439c622" xlink:to="loc_us-gaap_LetterOfCreditMember_019e0425-bb61-7fbe-8e6b-709292888f5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e041f-256f-7827-96b6-3fb9fffefd4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019dbda1-e465-760d-8535-5e49573ec91b" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e041f-256f-7827-96b6-3fb9fffefd4d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e041f-256f-7827-96b6-3fb9fffefd4d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e041f-256f-7827-96b6-3fb9fffefd4d" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e041f-256f-7827-96b6-3fb9fffefd4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e041f-7cc8-7ca6-a4bf-7419df9ef298" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e041f-256f-7827-96b6-3fb9fffefd4d" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e041f-7cc8-7ca6-a4bf-7419df9ef298" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_A2026RevolvingFacilityMember_019e0420-be37-7c8a-a2d3-616081ffcc63" xlink:href="ubnt-20260331.xsd#ubnt_A2026RevolvingFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e041f-7cc8-7ca6-a4bf-7419df9ef298" xlink:to="loc_ubnt_A2026RevolvingFacilityMember_019e0420-be37-7c8a-a2d3-616081ffcc63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019e0426-a764-7232-ae83-d4157f7e2c4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019dbda1-e465-760d-8535-5e49573ec91b" xlink:to="loc_us-gaap_VariableRateAxis_019e0426-a764-7232-ae83-d4157f7e2c4d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019e0426-a764-7232-ae83-d4157f7e2c4d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019e0426-a764-7232-ae83-d4157f7e2c4d" xlink:to="loc_us-gaap_VariableRateDomain_019e0426-a764-7232-ae83-d4157f7e2c4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019e0426-df7d-7c62-bb58-90149e52b968" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019e0426-a764-7232-ae83-d4157f7e2c4d" xlink:to="loc_us-gaap_VariableRateDomain_019e0426-df7d-7c62-bb58-90149e52b968" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_019e0427-0178-7255-aed6-ec2ae1e72537" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019e0426-df7d-7c62-bb58-90149e52b968" xlink:to="loc_us-gaap_BaseRateMember_019e0427-0178-7255-aed6-ec2ae1e72537" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019e042c-0915-7255-b148-ed255b86d764" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019e0426-df7d-7c62-bb58-90149e52b968" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019e042c-0915-7255-b148-ed255b86d764" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_OvernightBankFundingRateMember_019e042f-a63b-78de-bec5-fce36428d707" xlink:href="ubnt-20260331.xsd#ubnt_OvernightBankFundingRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019e0426-df7d-7c62-bb58-90149e52b968" xlink:to="loc_ubnt_OvernightBankFundingRateMember_019e042f-a63b-78de-bec5-fce36428d707" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_DailySimpleSOFRMember_019e0430-d9a0-7622-9794-13447cbeb767" xlink:href="ubnt-20260331.xsd#ubnt_DailySimpleSOFRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019e0426-df7d-7c62-bb58-90149e52b968" xlink:to="loc_ubnt_DailySimpleSOFRMember_019e0430-d9a0-7622-9794-13447cbeb767" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_ApplicableInterestRateMember_019e0432-7084-7d27-81fe-19c86d590876" xlink:href="ubnt-20260331.xsd#ubnt_ApplicableInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019e0426-df7d-7c62-bb58-90149e52b968" xlink:to="loc_ubnt_ApplicableInterestRateMember_019e0432-7084-7d27-81fe-19c86d590876" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e042a-5226-75ff-bf8a-9d029a6750ce" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019dbda1-e465-760d-8535-5e49573ec91b" xlink:to="loc_srt_RangeAxis_019e042a-5226-75ff-bf8a-9d029a6750ce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e042a-5226-75ff-bf8a-9d029a6750ce_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e042a-5226-75ff-bf8a-9d029a6750ce" xlink:to="loc_srt_RangeMember_019e042a-5226-75ff-bf8a-9d029a6750ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e042a-80b7-7a95-9cfc-43ec3aae00c3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e042a-5226-75ff-bf8a-9d029a6750ce" xlink:to="loc_srt_RangeMember_019e042a-80b7-7a95-9cfc-43ec3aae00c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e042a-a0fa-7819-a320-209ecbb6dac3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e042a-80b7-7a95-9cfc-43ec3aae00c3" xlink:to="loc_srt_MinimumMember_019e042a-a0fa-7819-a320-209ecbb6dac3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e042a-c4d8-7a8e-9a25-88f68eeb1190" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e042a-80b7-7a95-9cfc-43ec3aae00c3" xlink:to="loc_srt_MaximumMember_019e042a-c4d8-7a8e-9a25-88f68eeb1190" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_019dbda1-e465-7e9a-83b7-f5054d1ea1d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_019dbda1-e465-7e9a-83b7-f5054d1ea1d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019e041a-c8a3-7fce-b2ff-d7b6966fe5e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019e041a-c8a3-7fce-b2ff-d7b6966fe5e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019e0422-6415-7b02-9841-bf8624b756c7" xlink:href="ubnt-20260331.xsd#ubnt_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_ubnt_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019e0422-6415-7b02-9841-bf8624b756c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LinesOfCreditCurrent_019e0423-e76c-7035-ba4c-31872fc87cf4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LinesOfCreditCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_us-gaap_LinesOfCreditCurrent_019e0423-e76c-7035-ba4c-31872fc87cf4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019e0428-02fd-7b32-807e-a970afa9e327" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019e0428-02fd-7b32-807e-a970afa9e327" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_DebtInstrumentDebtDefaultBasisSpreadOverApplicableInterestRate_019e0432-bc8d-7a23-a72a-a3676eff8876" xlink:href="ubnt-20260331.xsd#ubnt_DebtInstrumentDebtDefaultBasisSpreadOverApplicableInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_ubnt_DebtInstrumentDebtDefaultBasisSpreadOverApplicableInterestRate_019e0432-bc8d-7a23-a72a-a3676eff8876" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019e0435-2530-71f6-a4b4-97c5c3028145" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019e0435-2530-71f6-a4b4-97c5c3028145" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_LineofCreditFacilityDebtIssuanceCostsPercentageAnnually_019e0438-3e99-7c07-a751-6a1c00d8c9c2" xlink:href="ubnt-20260331.xsd#ubnt_LineofCreditFacilityDebtIssuanceCostsPercentageAnnually"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_ubnt_LineofCreditFacilityDebtIssuanceCostsPercentageAnnually_019e0438-3e99-7c07-a751-6a1c00d8c9c2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RatioOfIndebtednessToNetCapital1_019e0439-6f72-7b07-8eb8-30a36038e760" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RatioOfIndebtednessToNetCapital1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_us-gaap_RatioOfIndebtednessToNetCapital1_019e0439-6f72-7b07-8eb8-30a36038e760" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_LineOfCreditFacilityCovenantTermsCoverageRatio_019e043a-6a3b-74a4-9d76-a2539e0af722" xlink:href="ubnt-20260331.xsd#ubnt_LineOfCreditFacilityCovenantTermsCoverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_ubnt_LineOfCreditFacilityCovenantTermsCoverageRatio_019e043a-6a3b-74a4-9d76-a2539e0af722" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ubnt_DebtCovenantMinimumUnrestrictedDomesticCashAndCashEquivalentsBalance_019e043e-ec9a-7648-9e82-ed94710c5d62" xlink:href="ubnt-20260331.xsd#ubnt_DebtCovenantMinimumUnrestrictedDomesticCashAndCashEquivalentsBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019dbda1-e465-7ad0-9c31-5dcf55328523" xlink:to="loc_ubnt_DebtCovenantMinimumUnrestrictedDomesticCashAndCashEquivalentsBalance_019e043e-ec9a-7648-9e82-ed94710c5d62" xlink:type="arc" order="10"/>
  </link:definitionLink>
</link:linkbase>
