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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019fcec5-9f86-7c49-8255-a144fd472841,g:2b1beb1d-96af-4830-b820-377676e538dd-->
<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://asteralabs.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="alab-20260930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fcec5-a03e-7ce7-97a2-767fc2c89b9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019fcec5-a03e-7a96-86e5-ddbc3c8d0e96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019fcec5-a03e-7ce7-97a2-767fc2c89b9b" xlink:to="loc_us-gaap_StatementTable_019fcec5-a03e-7a96-86e5-ddbc3c8d0e96" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fcec5-a03e-7b55-b85c-cf46d296cb89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fcec5-a03e-7a96-86e5-ddbc3c8d0e96" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fcec5-a03e-7b55-b85c-cf46d296cb89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fcec5-a03e-7b55-b85c-cf46d296cb89_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fcec5-a03e-7b55-b85c-cf46d296cb89" xlink:to="loc_us-gaap_EquityComponentDomain_019fcec5-a03e-7b55-b85c-cf46d296cb89_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fcec5-a03e-75e3-8f63-427cf9d8318e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fcec5-a03e-7b55-b85c-cf46d296cb89" xlink:to="loc_us-gaap_EquityComponentDomain_019fcec5-a03e-75e3-8f63-427cf9d8318e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fcec5-a03e-7c9b-a23b-ae57d007cd6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fcec5-a03e-75e3-8f63-427cf9d8318e" xlink:to="loc_us-gaap_CommonStockMember_019fcec5-a03e-7c9b-a23b-ae57d007cd6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019fcec5-a03e-7e01-830e-0ad6805b995b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fcec5-a03e-75e3-8f63-427cf9d8318e" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019fcec5-a03e-7e01-830e-0ad6805b995b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fcec5-a03e-7975-a10a-7034ec3566a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fcec5-a03e-75e3-8f63-427cf9d8318e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fcec5-a03e-7975-a10a-7034ec3566a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019fcec5-a03e-7be5-885e-71ff164178fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fcec5-a03e-75e3-8f63-427cf9d8318e" xlink:to="loc_us-gaap_RetainedEarningsMember_019fcec5-a03e-7be5-885e-71ff164178fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fcec5-a03e-7ce7-97a2-767fc2c89b9b" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fcec5-a03e-7997-9df7-6fd59201a8e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019fcec5-a03e-7997-9df7-6fd59201a8e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fcec5-a03e-760e-96b8-42c05ac84a25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockholdersEquity_019fcec5-a03e-760e-96b8-42c05ac84a25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019fcec5-a03e-7d5c-828b-0ceef5e38135" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019fcec5-a03e-7d5c-828b-0ceef5e38135" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationForfeited_01a17a00-97e5-7692-8b78-4fcd1ce80969" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationForfeited"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationForfeited_01a17a00-97e5-7692-8b78-4fcd1ce80969" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019fcec5-a03e-77fe-92b0-fb96fbe2fe58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019fcec5-a03e-77fe-92b0-fb96fbe2fe58" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019fcec5-a03e-707b-9fd0-0d3f4cb6fa2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019fcec5-a03e-707b-9fd0-0d3f4cb6fa2e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019fcec5-a03e-78a5-bebb-7b44bec9fa94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019fcec5-a03e-78a5-bebb-7b44bec9fa94" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CashlessExerciseOfWarrantsShares_019fcec5-a03e-79d0-b98a-01595c3e7be0" xlink:href="alab-20260930.xsd#alab_CashlessExerciseOfWarrantsShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_alab_CashlessExerciseOfWarrantsShares_019fcec5-a03e-79d0-b98a-01595c3e7be0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CashlessExerciseOfWarrantsValue_019fcec5-a03e-7b6f-8801-410765d9fa8b" xlink:href="alab-20260930.xsd#alab_CashlessExerciseOfWarrantsValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_alab_CashlessExerciseOfWarrantsValue_019fcec5-a03e-7b6f-8801-410765d9fa8b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019fcec5-a03e-7552-9c28-06b9f1c34006" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019fcec5-a03e-7552-9c28-06b9f1c34006" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_019fcec5-a03e-7996-9f58-001c1f44985d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_019fcec5-a03e-7996-9f58-001c1f44985d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019fcec5-a03e-7a33-bd89-0d84d865d255" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019fcec5-a03e-7a33-bd89-0d84d865d255" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019fcec5-a03e-7ce7-bd1a-2065e1c62c68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019fcec5-a03e-7ce7-bd1a-2065e1c62c68" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fcec5-a03e-7376-9fb7-1caf35852f6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fcec5-a03e-7376-9fb7-1caf35852f6f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_019fcec5-a03e-75fc-b1ed-7fb9f1b34c35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_019fcec5-a03e-75fc-b1ed-7fb9f1b34c35" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019fcec5-a03e-7eca-9227-b47db3c9f3af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019fcec5-a03e-7eca-9227-b47db3c9f3af" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fcec5-a03e-74c8-988f-a00c04bcb41f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcec5-a03e-71f0-b20e-276dfefb91d5" xlink:to="loc_us-gaap_NetIncomeLoss_019fcec5-a03e-74c8-988f-a00c04bcb41f" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fcec5-a03e-7f5b-8a36-b03bdc0bc46d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fcec5-a03e-720b-8ceb-609419b6c616" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/SegmentandGeographicalInformationNarrativeDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#SegmentandGeographicalInformationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/SegmentandGeographicalInformationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-76e0-8b4d-a846ab445c9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7377-bb0b-39e700fd3cd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-76e0-8b4d-a846ab445c9f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7377-bb0b-39e700fd3cd5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019fcec5-a03e-7b93-9966-a2dec23c9519" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7377-bb0b-39e700fd3cd5" xlink:to="loc_srt_StatementGeographicalAxis_019fcec5-a03e-7b93-9966-a2dec23c9519" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7b93-9966-a2dec23c9519_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019fcec5-a03e-7b93-9966-a2dec23c9519" xlink:to="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7b93-9966-a2dec23c9519_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7852-9feb-e226815e0352" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019fcec5-a03e-7b93-9966-a2dec23c9519" xlink:to="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7852-9feb-e226815e0352" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019fcec5-a03e-7846-8e6d-1d200f9e5eb0" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7852-9feb-e226815e0352" xlink:to="loc_country_US_019fcec5-a03e-7846-8e6d-1d200f9e5eb0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_TW_019fcec5-a03e-7129-8e7b-efd8b41b1f52" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_TW"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7852-9feb-e226815e0352" xlink:to="loc_country_TW_019fcec5-a03e-7129-8e7b-efd8b41b1f52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcec5-a03e-7fc1-a997-ab6ebc32e5af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7377-bb0b-39e700fd3cd5" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcec5-a03e-7fc1-a997-ab6ebc32e5af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7fc1-a997-ab6ebc32e5af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcec5-a03e-7fc1-a997-ab6ebc32e5af" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7fc1-a997-ab6ebc32e5af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7072-830f-303c32af01d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcec5-a03e-7fc1-a997-ab6ebc32e5af" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7072-830f-303c32af01d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentMember_019fcec5-a03e-721c-bcd8-4a3ddbc18a02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7072-830f-303c32af01d9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentMember_019fcec5-a03e-721c-bcd8-4a3ddbc18a02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcec5-a03e-7d06-b0b0-1b82dd25a640" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7377-bb0b-39e700fd3cd5" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcec5-a03e-7d06-b0b0-1b82dd25a640" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-7d06-b0b0-1b82dd25a640_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcec5-a03e-7d06-b0b0-1b82dd25a640" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-7d06-b0b0-1b82dd25a640_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-7897-9373-7ad0ef9146e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcec5-a03e-7d06-b0b0-1b82dd25a640" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-7897-9373-7ad0ef9146e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019fcec5-a03e-702c-bbc0-c7874937e3b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-7897-9373-7ad0ef9146e2" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019fcec5-a03e-702c-bbc0-c7874937e3b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019fcec5-a03e-7379-84e9-b915017b8104" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-76e0-8b4d-a846ab445c9f" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019fcec5-a03e-7379-84e9-b915017b8104" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_01a18a20-fd13-7042-a539-10134259e041" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-76e0-8b4d-a846ab445c9f" xlink:to="loc_us-gaap_NumberOfReportableSegments_01a18a20-fd13-7042-a539-10134259e041" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019fcec5-a03e-725c-9c8f-27d5c28e34e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-76e0-8b4d-a846ab445c9f" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019fcec5-a03e-725c-9c8f-27d5c28e34e7" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/SegmentandGeographicalInformationScheduleofSignificantExpenseCategoriesandAmountsRegularlyProvidedtotheCODMDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#SegmentandGeographicalInformationScheduleofSignificantExpenseCategoriesandAmountsRegularlyProvidedtotheCODMDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/SegmentandGeographicalInformationScheduleofSignificantExpenseCategoriesandAmountsRegularlyProvidedtotheCODMDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-7f0f-920e-b9aae3e02072" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7889-b68b-f209657f8f9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-7f0f-920e-b9aae3e02072" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7889-b68b-f209657f8f9d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fcec5-a03e-764f-9cdb-6bf6beea96e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7889-b68b-f209657f8f9d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fcec5-a03e-764f-9cdb-6bf6beea96e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fcec5-a03e-764f-9cdb-6bf6beea96e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fcec5-a03e-764f-9cdb-6bf6beea96e8" xlink:to="loc_us-gaap_SegmentDomain_019fcec5-a03e-764f-9cdb-6bf6beea96e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fcec5-a03e-7754-8a12-e72539bb7b31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fcec5-a03e-764f-9cdb-6bf6beea96e8" xlink:to="loc_us-gaap_SegmentDomain_019fcec5-a03e-7754-8a12-e72539bb7b31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ReportableSegmentMember_019fcec5-a03e-70ee-95f6-aea6b488d9de" xlink:href="alab-20260930.xsd#alab_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fcec5-a03e-7754-8a12-e72539bb7b31" xlink:to="loc_alab_ReportableSegmentMember_019fcec5-a03e-70ee-95f6-aea6b488d9de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fcec5-a03e-7b4f-9f51-a1a58d8f9d0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-7f0f-920e-b9aae3e02072" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fcec5-a03e-7b4f-9f51-a1a58d8f9d0d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fcec5-a03e-7c0b-94de-ec123fceffad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-7f0f-920e-b9aae3e02072" xlink:to="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fcec5-a03e-7c0b-94de-ec123fceffad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019fcec5-a03e-7a03-a706-fbe7bf3cfc09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fcec5-a03e-7c0b-94de-ec123fceffad" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019fcec5-a03e-7a03-a706-fbe7bf3cfc09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019fcec5-a03e-7857-afc3-9edc6f1bc13c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fcec5-a03e-7c0b-94de-ec123fceffad" xlink:to="loc_us-gaap_ShareBasedCompensation_019fcec5-a03e-7857-afc3-9edc6f1bc13c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_019fcec5-a03e-741d-9c06-64eb4e0cfda7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fcec5-a03e-7c0b-94de-ec123fceffad" xlink:to="loc_us-gaap_LaborAndRelatedExpense_019fcec5-a03e-741d-9c06-64eb4e0cfda7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019fcec5-a03e-7ad1-9741-fff0f5c0430c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fcec5-a03e-7c0b-94de-ec123fceffad" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019fcec5-a03e-7ad1-9741-fff0f5c0430c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fcec5-a03e-71f3-ae76-fe185fceda70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-7f0f-920e-b9aae3e02072" xlink:to="loc_us-gaap_NetIncomeLoss_019fcec5-a03e-71f3-ae76-fe185fceda70" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/SegmentandGeographicalInformationScheduleofRevenuebyGeographicLocationDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#SegmentandGeographicalInformationScheduleofRevenuebyGeographicLocationDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/SegmentandGeographicalInformationScheduleofRevenuebyGeographicLocationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-704c-8165-3128a939a270" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7e66-a2c2-621dd1c90dc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-704c-8165-3128a939a270" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7e66-a2c2-621dd1c90dc2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019fcec5-a03e-78de-9e15-36bf66b017c7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7e66-a2c2-621dd1c90dc2" xlink:to="loc_srt_StatementGeographicalAxis_019fcec5-a03e-78de-9e15-36bf66b017c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-78de-9e15-36bf66b017c7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019fcec5-a03e-78de-9e15-36bf66b017c7" xlink:to="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-78de-9e15-36bf66b017c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7a06-a2fa-912eb1dd3754" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019fcec5-a03e-78de-9e15-36bf66b017c7" xlink:to="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7a06-a2fa-912eb1dd3754" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_SG_019fcec5-a03e-7981-8e93-0de96ae6cbb4" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_SG"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7a06-a2fa-912eb1dd3754" xlink:to="loc_country_SG_019fcec5-a03e-7981-8e93-0de96ae6cbb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_019fcec5-a03e-747d-aa42-0eaee4894a91" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7a06-a2fa-912eb1dd3754" xlink:to="loc_country_CN_019fcec5-a03e-747d-aa42-0eaee4894a91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_TW_019fcec5-a03e-7ce6-bf18-4cf2b3e0ea76" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_TW"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7a06-a2fa-912eb1dd3754" xlink:to="loc_country_TW_019fcec5-a03e-7ce6-bf18-4cf2b3e0ea76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019fcec5-a03e-7ccf-a14c-7aa258ca50c0" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7a06-a2fa-912eb1dd3754" xlink:to="loc_country_US_019fcec5-a03e-7ccf-a14c-7aa258ca50c0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_019fcec5-a03e-78a5-a4bd-cf874bc955f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcec5-a03e-7a06-a2fa-912eb1dd3754" xlink:to="loc_us-gaap_NonUsMember_019fcec5-a03e-78a5-a4bd-cf874bc955f2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fcec5-a03e-71bf-94d0-fca0dcfbb29b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-704c-8165-3128a939a270" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fcec5-a03e-71bf-94d0-fca0dcfbb29b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/SegmentandGeographicalInformationScheduleofRevenueConcentrationRiskDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#SegmentandGeographicalInformationScheduleofRevenueConcentrationRiskDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/SegmentandGeographicalInformationScheduleofRevenueConcentrationRiskDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-7672-b715-23fb046a7b56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7f81-bd6e-25df0776faf7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-7672-b715-23fb046a7b56" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7f81-bd6e-25df0776faf7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019fcec5-a03e-7e6f-afe0-654e6564ef08" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7f81-bd6e-25df0776faf7" xlink:to="loc_srt_MajorCustomersAxis_019fcec5-a03e-7e6f-afe0-654e6564ef08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-7e6f-afe0-654e6564ef08_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019fcec5-a03e-7e6f-afe0-654e6564ef08" xlink:to="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-7e6f-afe0-654e6564ef08_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-758a-96af-72f9e798cd68" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019fcec5-a03e-7e6f-afe0-654e6564ef08" xlink:to="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-758a-96af-72f9e798cd68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CustomerAMember_019fcec5-a03e-7e45-9f7c-c69c17135a55" xlink:href="alab-20260930.xsd#alab_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-758a-96af-72f9e798cd68" xlink:to="loc_alab_CustomerAMember_019fcec5-a03e-7e45-9f7c-c69c17135a55" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CustomerBMember_019fcec5-a03e-7d35-8a6a-b2292bfaf69f" xlink:href="alab-20260930.xsd#alab_CustomerBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-758a-96af-72f9e798cd68" xlink:to="loc_alab_CustomerBMember_019fcec5-a03e-7d35-8a6a-b2292bfaf69f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CustomerCMember_019fcec5-a03e-7dfe-8ed6-1f33ae893b20" xlink:href="alab-20260930.xsd#alab_CustomerCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-758a-96af-72f9e798cd68" xlink:to="loc_alab_CustomerCMember_019fcec5-a03e-7dfe-8ed6-1f33ae893b20" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CustomerDMember_019fcec5-a03e-746e-ad92-4e8336d56f38" xlink:href="alab-20260930.xsd#alab_CustomerDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-758a-96af-72f9e798cd68" xlink:to="loc_alab_CustomerDMember_019fcec5-a03e-746e-ad92-4e8336d56f38" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CustomerEMember_019fcec5-a03e-7548-ad05-0c60c9daea6a" xlink:href="alab-20260930.xsd#alab_CustomerEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-758a-96af-72f9e798cd68" xlink:to="loc_alab_CustomerEMember_019fcec5-a03e-7548-ad05-0c60c9daea6a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CustomerFMember_01a01f46-d3c7-7c23-bd5e-63bb6a908883" xlink:href="alab-20260930.xsd#alab_CustomerFMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fcec5-a03e-758a-96af-72f9e798cd68" xlink:to="loc_alab_CustomerFMember_01a01f46-d3c7-7c23-bd5e-63bb6a908883" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcec5-a03e-7af2-af9e-47d3b1cd3182" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7f81-bd6e-25df0776faf7" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcec5-a03e-7af2-af9e-47d3b1cd3182" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7af2-af9e-47d3b1cd3182_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcec5-a03e-7af2-af9e-47d3b1cd3182" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7af2-af9e-47d3b1cd3182_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7a7a-b5a1-e1294cec0a2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcec5-a03e-7af2-af9e-47d3b1cd3182" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7a7a-b5a1-e1294cec0a2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_019fcec5-a03e-7888-a76b-cbf3619a4b3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7a7a-b5a1-e1294cec0a2d" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_019fcec5-a03e-7888-a76b-cbf3619a4b3b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019fcec5-a03e-7c88-9d71-b8cd1b81a2b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcec5-a03e-7a7a-b5a1-e1294cec0a2d" xlink:to="loc_us-gaap_AccountsReceivableMember_019fcec5-a03e-7c88-9d71-b8cd1b81a2b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcec5-a03e-78ca-9590-520ef0ab812c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcec5-a03e-7f81-bd6e-25df0776faf7" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcec5-a03e-78ca-9590-520ef0ab812c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-78ca-9590-520ef0ab812c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcec5-a03e-78ca-9590-520ef0ab812c" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-78ca-9590-520ef0ab812c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-73d4-97f3-42e157fb0085" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcec5-a03e-78ca-9590-520ef0ab812c" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-73d4-97f3-42e157fb0085" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019fcec5-a03e-76a9-98a7-53bf481a7b6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019fcec5-a03e-73d4-97f3-42e157fb0085" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019fcec5-a03e-76a9-98a7-53bf481a7b6a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019fcec5-a03e-7ae0-94f6-db92dae1e9bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcec5-a03e-7672-b715-23fb046a7b56" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019fcec5-a03e-7ae0-94f6-db92dae1e9bc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/MarketableSecuritiesScheduleofDebtSecuritiesAvailableForSaleDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#MarketableSecuritiesScheduleofDebtSecuritiesAvailableForSaleDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/MarketableSecuritiesScheduleofDebtSecuritiesAvailableForSaleDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7e73-b5dc-355f93094317" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcec5-a03e-7315-bdf9-7cdd5cb51628" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7e73-b5dc-355f93094317" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcec5-a03e-7315-bdf9-7cdd5cb51628" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019fcec5-a03e-75d7-aded-2daae110e0a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcec5-a03e-7315-bdf9-7cdd5cb51628" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019fcec5-a03e-75d7-aded-2daae110e0a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a03e-75d7-aded-2daae110e0a1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019fcec5-a03e-75d7-aded-2daae110e0a1" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a03e-75d7-aded-2daae110e0a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a03e-7b2c-83ae-89e586f8aea8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019fcec5-a03e-75d7-aded-2daae110e0a1" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a03e-7b2c-83ae-89e586f8aea8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashEquivalentsMember_019fcec5-a03e-7fa2-add0-477d5b68dd23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a03e-7b2c-83ae-89e586f8aea8" xlink:to="loc_us-gaap_CashEquivalentsMember_019fcec5-a03e-7fa2-add0-477d5b68dd23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019fcec5-a03e-7c6c-8b10-04f859a1dc38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsMember_019fcec5-a03e-7fa2-add0-477d5b68dd23" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019fcec5-a03e-7c6c-8b10-04f859a1dc38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_U.STreasuryAndAgencySecuritiesMember_01a13a98-183a-7451-b88b-28bbd8edddcb" xlink:href="alab-20260930.xsd#alab_U.STreasuryAndAgencySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsMember_019fcec5-a03e-7fa2-add0-477d5b68dd23" xlink:to="loc_alab_U.STreasuryAndAgencySecuritiesMember_01a13a98-183a-7451-b88b-28bbd8edddcb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019fcec5-a03e-7d5a-be98-87d5d9e06b36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsMember_019fcec5-a03e-7fa2-add0-477d5b68dd23" xlink:to="loc_us-gaap_CommercialPaperMember_019fcec5-a03e-7d5a-be98-87d5d9e06b36" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fcec5-a03e-7033-8294-720932268ddf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcec5-a03e-7315-bdf9-7cdd5cb51628" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fcec5-a03e-7033-8294-720932268ddf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a03e-7033-8294-720932268ddf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcec5-a03e-7033-8294-720932268ddf" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a03e-7033-8294-720932268ddf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a03e-73ce-aa62-32714d6800b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcec5-a03e-7033-8294-720932268ddf" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a03e-73ce-aa62-32714d6800b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_MarketableSecuritiesMember_019fcec5-a03e-72ee-9d2c-7c4b1bdfa7ed" xlink:href="alab-20260930.xsd#alab_MarketableSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a03e-73ce-aa62-32714d6800b4" xlink:to="loc_alab_MarketableSecuritiesMember_019fcec5-a03e-72ee-9d2c-7c4b1bdfa7ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_U.STreasuryAndAgencySecuritiesMember_019fcec5-a03e-7bdf-9250-7ad431a05d38" xlink:href="alab-20260930.xsd#alab_U.STreasuryAndAgencySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alab_MarketableSecuritiesMember_019fcec5-a03e-72ee-9d2c-7c4b1bdfa7ed" xlink:to="loc_alab_U.STreasuryAndAgencySecuritiesMember_019fcec5-a03e-7bdf-9250-7ad431a05d38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019fcec5-a03e-7ba8-b6b9-91573ed62e4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alab_MarketableSecuritiesMember_019fcec5-a03e-72ee-9d2c-7c4b1bdfa7ed" xlink:to="loc_us-gaap_CommercialPaperMember_019fcec5-a03e-7ba8-b6b9-91573ed62e4a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fcec5-a03e-7419-b1b6-35178d1ea518" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alab_MarketableSecuritiesMember_019fcec5-a03e-72ee-9d2c-7c4b1bdfa7ed" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fcec5-a03e-7419-b1b6-35178d1ea518" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019fcec5-a03e-7e52-9882-4f0b3644bcd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7e73-b5dc-355f93094317" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019fcec5-a03e-7e52-9882-4f0b3644bcd0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019fcec5-a03e-7d0a-bafb-a564926bd4f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7e73-b5dc-355f93094317" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019fcec5-a03e-7d0a-bafb-a564926bd4f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fcec5-a03e-7dff-a3fb-83c0b32cfb83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7e73-b5dc-355f93094317" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fcec5-a03e-7dff-a3fb-83c0b32cfb83" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fcec5-a03e-7327-b4e6-085f8e026c9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7e73-b5dc-355f93094317" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fcec5-a03e-7327-b4e6-085f8e026c9a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/MarketableSecuritiesScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#MarketableSecuritiesScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/MarketableSecuritiesScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7191-a59c-cd627406535f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcec5-a03e-783a-8757-7fe2070f0145" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7191-a59c-cd627406535f" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcec5-a03e-783a-8757-7fe2070f0145" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019fcec5-a03e-71f2-90bc-8043b13b2a77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcec5-a03e-783a-8757-7fe2070f0145" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019fcec5-a03e-71f2-90bc-8043b13b2a77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fcec5-a03e-71f2-90bc-8043b13b2a77_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019fcec5-a03e-71f2-90bc-8043b13b2a77" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fcec5-a03e-71f2-90bc-8043b13b2a77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fcec5-a03e-7652-bf5c-d605bdf38ff3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019fcec5-a03e-71f2-90bc-8043b13b2a77" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fcec5-a03e-7652-bf5c-d605bdf38ff3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CashEquivalentsAndMarketableSecuritiesMember_019fcec5-a03e-7b26-b025-4dd4379d2ffa" xlink:href="alab-20260930.xsd#alab_CashEquivalentsAndMarketableSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fcec5-a03e-7652-bf5c-d605bdf38ff3" xlink:to="loc_alab_CashEquivalentsAndMarketableSecuritiesMember_019fcec5-a03e-7b26-b025-4dd4379d2ffa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fcec5-a03e-7da5-819d-2b3222041157" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7191-a59c-cd627406535f" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fcec5-a03e-7da5-819d-2b3222041157" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_019fcec5-a03e-7fe7-b44c-faabf3043a7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fcec5-a03e-7da5-819d-2b3222041157" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_019fcec5-a03e-7fe7-b44c-faabf3043a7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_019fcec5-a03e-7f9a-b228-d6a1a8c4f18c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fcec5-a03e-7da5-819d-2b3222041157" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_019fcec5-a03e-7f9a-b228-d6a1a8c4f18c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019fcec5-a03e-7259-a083-65aa95630e8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fcec5-a03e-7da5-819d-2b3222041157" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019fcec5-a03e-7259-a083-65aa95630e8b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fcec5-a03e-7ebf-be73-a636295a852e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcec5-a03e-7191-a59c-cd627406535f" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fcec5-a03e-7ebf-be73-a636295a852e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_019fcec5-a03e-76d1-8869-161d676dd86c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fcec5-a03e-7ebf-be73-a636295a852e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_019fcec5-a03e-76d1-8869-161d676dd86c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_019fcec5-a0e6-7187-a8c5-e0cb850e8dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fcec5-a03e-7ebf-be73-a636295a852e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_019fcec5-a0e6-7187-a8c5-e0cb850e8dc6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fcec5-a0e6-7b78-80d4-e12440ce24b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fcec5-a03e-7ebf-be73-a636295a852e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fcec5-a0e6-7b78-80d4-e12440ce24b6" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/FairValueMeasurementsScheduleofFairValueAssetsMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#FairValueMeasurementsScheduleofFairValueAssetsMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/FairValueMeasurementsScheduleofFairValueAssetsMeasuredonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcec5-a0e6-708e-8892-f802b904b2f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcec5-a0e6-7863-8670-7627b76fc044" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcec5-a0e6-708e-8892-f802b904b2f9" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcec5-a0e6-7863-8670-7627b76fc044" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fcec5-a0e6-7bef-b1c7-bedfd3e8c088" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcec5-a0e6-7863-8670-7627b76fc044" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fcec5-a0e6-7bef-b1c7-bedfd3e8c088" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcec5-a0e6-7bef-b1c7-bedfd3e8c088_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fcec5-a0e6-7bef-b1c7-bedfd3e8c088" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcec5-a0e6-7bef-b1c7-bedfd3e8c088_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcec5-a0e6-7d60-b506-03b21eeffa96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fcec5-a0e6-7bef-b1c7-bedfd3e8c088" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcec5-a0e6-7d60-b506-03b21eeffa96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fcec5-a0e6-74fc-b070-fb382e79c179" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcec5-a0e6-7d60-b506-03b21eeffa96" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fcec5-a0e6-74fc-b070-fb382e79c179" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fcec5-a0e6-7862-a010-7ff617e7a983" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcec5-a0e6-7d60-b506-03b21eeffa96" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fcec5-a0e6-7862-a010-7ff617e7a983" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019fcec5-a0e6-7327-8369-cf5b0e9c6264" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcec5-a0e6-7863-8670-7627b76fc044" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019fcec5-a0e6-7327-8369-cf5b0e9c6264" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a0e6-7327-8369-cf5b0e9c6264_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019fcec5-a0e6-7327-8369-cf5b0e9c6264" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a0e6-7327-8369-cf5b0e9c6264_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a0e6-7164-ab70-900a7e7c5c94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019fcec5-a0e6-7327-8369-cf5b0e9c6264" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a0e6-7164-ab70-900a7e7c5c94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019fcec5-a0e6-75f0-9ff4-a81b3ed15d1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a0e6-7164-ab70-900a7e7c5c94" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019fcec5-a0e6-75f0-9ff4-a81b3ed15d1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_U.STreasuryAndAgencySecuritiesMember_01a13a99-4d3c-7a2e-ad45-15b86f6778d5" xlink:href="alab-20260930.xsd#alab_U.STreasuryAndAgencySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a0e6-7164-ab70-900a7e7c5c94" xlink:to="loc_alab_U.STreasuryAndAgencySecuritiesMember_01a13a99-4d3c-7a2e-ad45-15b86f6778d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019fcec5-a0e6-750e-a798-fd9c86b9420f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fcec5-a0e6-7164-ab70-900a7e7c5c94" xlink:to="loc_us-gaap_CommercialPaperMember_019fcec5-a0e6-750e-a798-fd9c86b9420f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fcec5-a0e6-73fd-8073-c41a00f82bea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcec5-a0e6-7863-8670-7627b76fc044" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fcec5-a0e6-73fd-8073-c41a00f82bea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a0e6-73fd-8073-c41a00f82bea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcec5-a0e6-73fd-8073-c41a00f82bea" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a0e6-73fd-8073-c41a00f82bea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a0e6-7bae-81c1-b3354063f138" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcec5-a0e6-73fd-8073-c41a00f82bea" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a0e6-7bae-81c1-b3354063f138" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_U.STreasuryAndAgencySecuritiesMember_019fcec5-a0e6-7508-be82-4ddb4c182a1e" xlink:href="alab-20260930.xsd#alab_U.STreasuryAndAgencySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a0e6-7bae-81c1-b3354063f138" xlink:to="loc_alab_U.STreasuryAndAgencySecuritiesMember_019fcec5-a0e6-7508-be82-4ddb4c182a1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019fcec5-a0e6-74f1-bb9a-77e004378f20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a0e6-7bae-81c1-b3354063f138" xlink:to="loc_us-gaap_CommercialPaperMember_019fcec5-a0e6-74f1-bb9a-77e004378f20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fcec5-a0e6-7064-8fc7-7aec254d1859" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcec5-a0e6-7bae-81c1-b3354063f138" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fcec5-a0e6-7064-8fc7-7aec254d1859" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019fcec5-a0e6-72d8-a354-2e89d70bc35d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcec5-a0e6-708e-8892-f802b904b2f9" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019fcec5-a0e6-72d8-a354-2e89d70bc35d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fcec5-a0e6-7769-b8a6-ba21dd59b757" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcec5-a0e6-708e-8892-f802b904b2f9" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fcec5-a0e6-7769-b8a6-ba21dd59b757" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/CondensedConsolidatedBalanceSheetComponentsScheduleofPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#CondensedConsolidatedBalanceSheetComponentsScheduleofPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/CondensedConsolidatedBalanceSheetComponentsScheduleofPropertyandEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fcec5-a0e6-7e50-87d7-c090016d4478" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fcec5-a0e6-722b-aaca-1c3927e25f8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fcec5-a0e6-7e50-87d7-c090016d4478" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fcec5-a0e6-722b-aaca-1c3927e25f8d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fcec5-a0e6-7917-a00a-177d40dfa28c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fcec5-a0e6-722b-aaca-1c3927e25f8d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fcec5-a0e6-7917-a00a-177d40dfa28c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7917-a00a-177d40dfa28c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fcec5-a0e6-7917-a00a-177d40dfa28c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7917-a00a-177d40dfa28c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7e07-9a27-5a3b24ab0f65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fcec5-a0e6-7917-a00a-177d40dfa28c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7e07-9a27-5a3b24ab0f65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019fcec5-a0e6-79cb-8756-2294c06838fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7e07-9a27-5a3b24ab0f65" xlink:to="loc_us-gaap_ConstructionInProgressMember_019fcec5-a0e6-79cb-8756-2294c06838fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ProductionAndManufacturingEquipmentMember_019fcec5-a0e6-7b1d-b014-35e28e5e7e21" xlink:href="alab-20260930.xsd#alab_ProductionAndManufacturingEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7e07-9a27-5a3b24ab0f65" xlink:to="loc_alab_ProductionAndManufacturingEquipmentMember_019fcec5-a0e6-7b1d-b014-35e28e5e7e21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquipmentMember_019fcec5-a0e6-74a5-b83a-342e00d1cfb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7e07-9a27-5a3b24ab0f65" xlink:to="loc_us-gaap_EquipmentMember_019fcec5-a0e6-74a5-b83a-342e00d1cfb3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019fcec5-a0e6-7148-b1ae-fd15c895c0cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7e07-9a27-5a3b24ab0f65" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019fcec5-a0e6-7148-b1ae-fd15c895c0cc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherMachineryAndEquipmentMember_019fcec5-a0e6-77e8-a8ed-f05b5a1fa254" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherMachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fcec5-a0e6-7e07-9a27-5a3b24ab0f65" xlink:to="loc_us-gaap_OtherMachineryAndEquipmentMember_019fcec5-a0e6-77e8-a8ed-f05b5a1fa254" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019fcec5-a0e6-7b00-8b66-33409323b22a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fcec5-a0e6-7e50-87d7-c090016d4478" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019fcec5-a0e6-7b00-8b66-33409323b22a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019fcec5-a0e6-7a5b-810d-6c896c29a69f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fcec5-a0e6-7e50-87d7-c090016d4478" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019fcec5-a0e6-7a5b-810d-6c896c29a69f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019fcec5-a0e6-79c6-83a5-73ed1056dc67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fcec5-a0e6-7e50-87d7-c090016d4478" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019fcec5-a0e6-79c6-83a5-73ed1056dc67" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/BusinessCombinationsDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#BusinessCombinationsDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/BusinessCombinationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fcec5-a0e6-7c73-b274-8ff83029b05d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fcec5-a0e6-7dfd-ba31-55f82fc0ee93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcec5-a0e6-7c73-b274-8ff83029b05d" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fcec5-a0e6-7dfd-ba31-55f82fc0ee93" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e6-7571-b10e-19272218c6d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fcec5-a0e6-7dfd-ba31-55f82fc0ee93" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e6-7571-b10e-19272218c6d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e6-7571-b10e-19272218c6d2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e6-7571-b10e-19272218c6d2" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e6-7571-b10e-19272218c6d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e6-78f4-8bd1-3168bd648de4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e6-7571-b10e-19272218c6d2" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e6-78f4-8bd1-3168bd648de4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_PrivatelyHeldCompanyMember_019fcec5-a0e6-7f57-9911-6fcd6c8d68c0" xlink:href="alab-20260930.xsd#alab_PrivatelyHeldCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e6-78f4-8bd1-3168bd648de4" xlink:to="loc_alab_PrivatelyHeldCompanyMember_019fcec5-a0e6-7f57-9911-6fcd6c8d68c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fcec5-a0e6-75fb-b58f-c41f85162545" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcec5-a0e6-7c73-b274-8ff83029b05d" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fcec5-a0e6-75fb-b58f-c41f85162545" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fcec5-a0e6-7c18-a441-dc9e607bd463" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcec5-a0e6-7c73-b274-8ff83029b05d" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fcec5-a0e6-7c18-a441-dc9e607bd463" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_BusinessCombinationContingentConsiderationHoldbackIndemnities_019fcec5-a0e6-7897-9cfb-af84fb399578" xlink:href="alab-20260930.xsd#alab_BusinessCombinationContingentConsiderationHoldbackIndemnities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcec5-a0e6-7c73-b274-8ff83029b05d" xlink:to="loc_alab_BusinessCombinationContingentConsiderationHoldbackIndemnities_019fcec5-a0e6-7897-9cfb-af84fb399578" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fcec5-a0e6-7227-83d2-a1e7b196e11d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcec5-a0e6-7c73-b274-8ff83029b05d" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fcec5-a0e6-7227-83d2-a1e7b196e11d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fcec5-a0e6-715c-8cce-5957bd86f00a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcec5-a0e6-7c73-b274-8ff83029b05d" xlink:to="loc_us-gaap_Goodwill_019fcec5-a0e6-715c-8cce-5957bd86f00a" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/CommonStockWarrantsNarrativeDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#CommonStockWarrantsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/CommonStockWarrantsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_019fcec5-a0e7-790d-af42-0b3dd6abaafc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019fcec5-a0e7-790d-af42-0b3dd6abaafc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019fcec5-a0e7-73a9-b35d-d5cd540a1e13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019fcec5-a0e7-790d-af42-0b3dd6abaafc" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019fcec5-a0e7-73a9-b35d-d5cd540a1e13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-73a9-b35d-d5cd540a1e13_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019fcec5-a0e7-73a9-b35d-d5cd540a1e13" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-73a9-b35d-d5cd540a1e13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7ef6-8336-c2c3dc17ee06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019fcec5-a0e7-73a9-b35d-d5cd540a1e13" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7ef6-8336-c2c3dc17ee06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_A2021WarrantMember_019fcec5-a0e7-730c-9658-db5e72282216" xlink:href="alab-20260930.xsd#alab_A2021WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7ef6-8336-c2c3dc17ee06" xlink:to="loc_alab_A2021WarrantMember_019fcec5-a0e7-730c-9658-db5e72282216" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CustomerWarrantMember_019fcec5-a0e7-7f0c-9e87-f031758220a2" xlink:href="alab-20260930.xsd#alab_CustomerWarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7ef6-8336-c2c3dc17ee06" xlink:to="loc_alab_CustomerWarrantMember_019fcec5-a0e7-7f0c-9e87-f031758220a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_A2023WarrantMember_019fcec5-a0e7-7313-8f59-3af12184f561" xlink:href="alab-20260930.xsd#alab_A2023WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7ef6-8336-c2c3dc17ee06" xlink:to="loc_alab_A2023WarrantMember_019fcec5-a0e7-7313-8f59-3af12184f561" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_A2026WarrantMember_019fcec5-a0e7-75bb-a740-f174c46ccecb" xlink:href="alab-20260930.xsd#alab_A2026WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7ef6-8336-c2c3dc17ee06" xlink:to="loc_alab_A2026WarrantMember_019fcec5-a0e7-75bb-a740-f174c46ccecb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fcec5-a0e7-77be-9191-1cb828920152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fcec5-a0e7-77be-9191-1cb828920152" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fcec5-a0e7-721c-926e-007fd918fbf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fcec5-a0e7-721c-926e-007fd918fbf1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_CashlessExerciseOfWarrantsShares_019fcec5-a0e7-785c-bcc2-9d46ef0ec60d" xlink:href="alab-20260930.xsd#alab_CashlessExerciseOfWarrantsShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_alab_CashlessExerciseOfWarrantsShares_019fcec5-a0e7-785c-bcc2-9d46ef0ec60d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ClassOfWarrantOrRightExercisableTerm_019fcec5-a0e7-7188-a5f5-9a771f50f49a" xlink:href="alab-20260930.xsd#alab_ClassOfWarrantOrRightExercisableTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_alab_ClassOfWarrantOrRightExercisableTerm_019fcec5-a0e7-7188-a5f5-9a771f50f49a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ClassOfWarrantsGrantDateFairValuePerShare_019fcec5-a0e7-726c-b56d-0929272947d0" xlink:href="alab-20260930.xsd#alab_ClassOfWarrantsGrantDateFairValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_alab_ClassOfWarrantsGrantDateFairValuePerShare_019fcec5-a0e7-726c-b56d-0929272947d0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ClassOfWarrantsGrantDateFairValue_019fcec5-a0e7-7319-bba4-b12b0b899ac3" xlink:href="alab-20260930.xsd#alab_ClassOfWarrantsGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_alab_ClassOfWarrantsGrantDateFairValue_019fcec5-a0e7-7319-bba4-b12b0b899ac3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ClassOfWarrantOrRightSharesIssuable_019fcec5-a0e7-7977-979d-2c326a0d1df5" xlink:href="alab-20260930.xsd#alab_ClassOfWarrantOrRightSharesIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_alab_ClassOfWarrantOrRightSharesIssuable_019fcec5-a0e7-7977-979d-2c326a0d1df5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ClassOfWarrantOrRightEligibleForVesting_019fcec5-a0e7-7a14-95f9-35cb5734b961" xlink:href="alab-20260930.xsd#alab_ClassOfWarrantOrRightEligibleForVesting"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_alab_ClassOfWarrantOrRightEligibleForVesting_019fcec5-a0e7-7a14-95f9-35cb5734b961" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ClassOfWarrantOrRightExercisesDuringPeriod_019fcec5-a0e7-72a6-b03d-5a59257d2633" xlink:href="alab-20260930.xsd#alab_ClassOfWarrantOrRightExercisesDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_alab_ClassOfWarrantOrRightExercisesDuringPeriod_019fcec5-a0e7-72a6-b03d-5a59257d2633" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_ClassOfWarrantsOrRightContraRevenue_019fcec5-a0e7-707a-9a31-ea3b47df2800" xlink:href="alab-20260930.xsd#alab_ClassOfWarrantsOrRightContraRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-72fe-a870-f6d0fc064449" xlink:to="loc_alab_ClassOfWarrantsOrRightContraRevenue_019fcec5-a0e7-707a-9a31-ea3b47df2800" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/CommonStockWarrantsScheduleofGrantDateFairValuesof2026WarrantDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#CommonStockWarrantsScheduleofGrantDateFairValuesof2026WarrantDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/CommonStockWarrantsScheduleofGrantDateFairValuesof2026WarrantDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-70c9-8614-51a4ad2446b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_019fcec5-a0e7-7288-89b9-af299fc4b865" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-70c9-8614-51a4ad2446b0" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019fcec5-a0e7-7288-89b9-af299fc4b865" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019fcec5-a0e7-7e95-ac2e-8b4a171d3fb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019fcec5-a0e7-7288-89b9-af299fc4b865" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019fcec5-a0e7-7e95-ac2e-8b4a171d3fb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7e95-ac2e-8b4a171d3fb9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019fcec5-a0e7-7e95-ac2e-8b4a171d3fb9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7e95-ac2e-8b4a171d3fb9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7f42-9d36-f9c922dee430" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019fcec5-a0e7-7e95-ac2e-8b4a171d3fb9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7f42-9d36-f9c922dee430" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_A2026WarrantMember_019fcec5-a0e7-76f9-b592-18b516c4c7ee" xlink:href="alab-20260930.xsd#alab_A2026WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fcec5-a0e7-7f42-9d36-f9c922dee430" xlink:to="loc_alab_A2026WarrantMember_019fcec5-a0e7-76f9-b592-18b516c4c7ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019fcec5-a0e7-71b4-bae1-e2de8828009e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019fcec5-a0e7-7288-89b9-af299fc4b865" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019fcec5-a0e7-71b4-bae1-e2de8828009e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-71b4-bae1-e2de8828009e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019fcec5-a0e7-71b4-bae1-e2de8828009e" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-71b4-bae1-e2de8828009e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-7387-9d5a-0cda6e827fa4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019fcec5-a0e7-71b4-bae1-e2de8828009e" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-7387-9d5a-0cda6e827fa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019fcec5-a0e7-7daf-9987-c272902e3a93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedDividendRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-7387-9d5a-0cda6e827fa4" xlink:to="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019fcec5-a0e7-7daf-9987-c272902e3a93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019fcec5-a0e7-7601-9550-da8e75c19dd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-7387-9d5a-0cda6e827fa4" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019fcec5-a0e7-7601-9550-da8e75c19dd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019fcec5-a0e7-71a9-bc58-68f19cec0cb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-7387-9d5a-0cda6e827fa4" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019fcec5-a0e7-71a9-bc58-68f19cec0cb9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019fcec5-a0e7-7283-b25f-d918a492d5ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-7387-9d5a-0cda6e827fa4" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019fcec5-a0e7-7283-b25f-d918a492d5ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_019fcec5-a0e7-71d3-b15c-443da94adc58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fcec5-a0e7-7387-9d5a-0cda6e827fa4" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_019fcec5-a0e7-71d3-b15c-443da94adc58" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019fcec5-a0e7-74a8-a198-8d2fe03e249d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fcec5-a0e7-70c9-8614-51a4ad2446b0" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019fcec5-a0e7-74a8-a198-8d2fe03e249d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019fcec5-a0e7-78ca-a5ed-708a5ad74cee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019fcec5-a0e7-7fb4-93d7-b731bac96f11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019fcec5-a0e7-78ca-a5ed-708a5ad74cee" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019fcec5-a0e7-7fb4-93d7-b731bac96f11" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fcec5-a0e7-7326-8093-c5ec775400b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019fcec5-a0e7-7fb4-93d7-b731bac96f11" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fcec5-a0e7-7326-8093-c5ec775400b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e7-79b4-8d53-6f302b8dd916" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019fcec5-a0e7-7fb4-93d7-b731bac96f11" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e7-79b4-8d53-6f302b8dd916" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-79b4-8d53-6f302b8dd916_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e7-79b4-8d53-6f302b8dd916" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-79b4-8d53-6f302b8dd916_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-7ab8-bc56-68bfda0d2e0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e7-79b4-8d53-6f302b8dd916" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-7ab8-bc56-68bfda0d2e0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_PrivatelyHeldCompanyMember_019fcec5-a0e7-7e19-aa6b-dc2f1fa0d194" xlink:href="alab-20260930.xsd#alab_PrivatelyHeldCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-7ab8-bc56-68bfda0d2e0e" xlink:to="loc_alab_PrivatelyHeldCompanyMember_019fcec5-a0e7-7e19-aa6b-dc2f1fa0d194" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcec5-a0e7-70d3-8385-fe613f343ed2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019fcec5-a0e7-78ca-a5ed-708a5ad74cee" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcec5-a0e7-70d3-8385-fe613f343ed2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fcec5-a0e7-73c2-bb71-43f3e9284959" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019fcec5-a0e7-78ca-a5ed-708a5ad74cee" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fcec5-a0e7-73c2-bb71-43f3e9284959" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails_1" xlink:type="simple" xlink:href="alab-20260930.xsd#StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails_1"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/StockBasedCompensationScheduleofStockBasedCompensationExpenseDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019fcec5-a0e7-78ca-a5ed-708a5ad74cee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019fcec5-a0e7-7fb4-93d7-b731bac96f11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019fcec5-a0e7-78ca-a5ed-708a5ad74cee" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019fcec5-a0e7-7fb4-93d7-b731bac96f11" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e7-79b4-8d53-6f302b8dd916" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019fcec5-a0e7-7fb4-93d7-b731bac96f11" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e7-79b4-8d53-6f302b8dd916" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-79b4-8d53-6f302b8dd916_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e7-79b4-8d53-6f302b8dd916" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-79b4-8d53-6f302b8dd916_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-7ab8-bc56-68bfda0d2e0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcec5-a0e7-79b4-8d53-6f302b8dd916" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-7ab8-bc56-68bfda0d2e0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_PrivatelyHeldCompanyMember_019fcec5-a0e7-7e19-aa6b-dc2f1fa0d194" xlink:href="alab-20260930.xsd#alab_PrivatelyHeldCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcec5-a0e7-7ab8-bc56-68bfda0d2e0e" xlink:to="loc_alab_PrivatelyHeldCompanyMember_019fcec5-a0e7-7e19-aa6b-dc2f1fa0d194" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcec5-a0e7-70d3-8385-fe613f343ed2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019fcec5-a0e7-78ca-a5ed-708a5ad74cee" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcec5-a0e7-70d3-8385-fe613f343ed2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fcec5-a0e7-73c2-bb71-43f3e9284959" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019fcec5-a0e7-78ca-a5ed-708a5ad74cee" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fcec5-a0e7-73c2-bb71-43f3e9284959" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/StockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#StockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-7d44-8a8f-b90c35e5293c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcec5-a0e7-7b13-9395-973803179e18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-7d44-8a8f-b90c35e5293c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcec5-a0e7-7b13-9395-973803179e18" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fcec5-a0e7-7089-8ab8-034fcd4d440d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcec5-a0e7-7b13-9395-973803179e18" xlink:to="loc_us-gaap_AwardTypeAxis_019fcec5-a0e7-7089-8ab8-034fcd4d440d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7089-8ab8-034fcd4d440d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fcec5-a0e7-7089-8ab8-034fcd4d440d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7089-8ab8-034fcd4d440d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7a91-854e-4cb9783d7b67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fcec5-a0e7-7089-8ab8-034fcd4d440d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7a91-854e-4cb9783d7b67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019fcec5-a0e7-7975-96f5-a6f2af06bce0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7a91-854e-4cb9783d7b67" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019fcec5-a0e7-7975-96f5-a6f2af06bce0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019fcec5-a0e7-7fb6-aede-2ce88d715241" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7a91-854e-4cb9783d7b67" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019fcec5-a0e7-7fb6-aede-2ce88d715241" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019fcec5-a0e7-720c-b648-880d5e2a7b12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7a91-854e-4cb9783d7b67" xlink:to="loc_us-gaap_PerformanceSharesMember_019fcec5-a0e7-720c-b648-880d5e2a7b12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019fcec5-a0e7-7f71-8d77-3d205eb0eb71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-7d44-8a8f-b90c35e5293c" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019fcec5-a0e7-7f71-8d77-3d205eb0eb71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019fcec5-a0e7-7d44-a900-fab4293318d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-7d44-8a8f-b90c35e5293c" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019fcec5-a0e7-7d44-a900-fab4293318d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019fcec5-a0e7-7fc2-bc67-af153529d952" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-7d44-8a8f-b90c35e5293c" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019fcec5-a0e7-7fc2-bc67-af153529d952" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/StockBasedCompensationScheduleofRestrictedStockUnitsActivityandPerformanceStockUnitsActivityDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#StockBasedCompensationScheduleofRestrictedStockUnitsActivityandPerformanceStockUnitsActivityDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/StockBasedCompensationScheduleofRestrictedStockUnitsActivityandPerformanceStockUnitsActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-745f-b330-41ba97e814c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcec5-a0e7-7d23-b766-c23cb6a350d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-745f-b330-41ba97e814c0" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcec5-a0e7-7d23-b766-c23cb6a350d9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fcec5-a0e7-75bf-8cca-08e10c9fa7dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcec5-a0e7-7d23-b766-c23cb6a350d9" xlink:to="loc_us-gaap_AwardTypeAxis_019fcec5-a0e7-75bf-8cca-08e10c9fa7dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-75bf-8cca-08e10c9fa7dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fcec5-a0e7-75bf-8cca-08e10c9fa7dc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-75bf-8cca-08e10c9fa7dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7151-b518-a6b92bba90a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fcec5-a0e7-75bf-8cca-08e10c9fa7dc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7151-b518-a6b92bba90a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019fcec5-a0e7-7852-8a60-29d4de6dd0a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7151-b518-a6b92bba90a1" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019fcec5-a0e7-7852-8a60-29d4de6dd0a9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019fcec5-a0e7-7549-85dd-0c2e066e7459" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcec5-a0e7-7151-b518-a6b92bba90a1" xlink:to="loc_us-gaap_PerformanceSharesMember_019fcec5-a0e7-7549-85dd-0c2e066e7459" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019fcec5-a0e7-79ed-8953-6cc1c74dac43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-745f-b330-41ba97e814c0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019fcec5-a0e7-79ed-8953-6cc1c74dac43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019fcec5-a0e7-7e66-a07a-dcb28a8bafcb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019fcec5-a0e7-79ed-8953-6cc1c74dac43" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019fcec5-a0e7-7e66-a07a-dcb28a8bafcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019fcec5-a0e7-70a4-836e-b6dd62625b64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019fcec5-a0e7-79ed-8953-6cc1c74dac43" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019fcec5-a0e7-70a4-836e-b6dd62625b64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019fcec5-a0e7-73b6-b760-eb33e041a3d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019fcec5-a0e7-79ed-8953-6cc1c74dac43" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019fcec5-a0e7-73b6-b760-eb33e041a3d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019fcec5-a0e7-703d-9fea-0ca7371f31bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_019fcec5-a0e7-79ed-8953-6cc1c74dac43" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019fcec5-a0e7-703d-9fea-0ca7371f31bb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019fcec5-a0e7-78d6-8af5-6443133001c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcec5-a0e7-78ca-a4c6-4129ad953f91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcec5-a0e7-745f-b330-41ba97e814c0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcec5-a0e7-78ca-a4c6-4129ad953f91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019fcec5-a0e7-799d-ad37-9e781940b348" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcec5-a0e7-78ca-a4c6-4129ad953f91" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019fcec5-a0e7-799d-ad37-9e781940b348" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019fcec5-a0e7-7b29-ab3d-c22b46754e3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcec5-a0e7-78ca-a4c6-4129ad953f91" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019fcec5-a0e7-7b29-ab3d-c22b46754e3c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019fcec5-a0e7-71f6-b955-f5c250e01e42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcec5-a0e7-78ca-a4c6-4129ad953f91" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019fcec5-a0e7-71f6-b955-f5c250e01e42" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019fcec5-a0e7-7d8c-a9b5-67fa61087616" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcec5-a0e7-78ca-a4c6-4129ad953f91" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019fcec5-a0e7-7d8c-a9b5-67fa61087616" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019fcec5-a0e7-7ae2-99b5-599adcb746e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://asteralabs.com/role/NetIncomeperShareScheduleofAntiDilutivePotentialSharesDetails" xlink:type="simple" xlink:href="alab-20260930.xsd#NetIncomeperShareScheduleofAntiDilutivePotentialSharesDetails"/>
  <link:definitionLink xlink:role="http://asteralabs.com/role/NetIncomeperShareScheduleofAntiDilutivePotentialSharesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019fcec5-a0e7-7340-b833-f7b32dfeefe5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019fcec5-a0e7-7cce-ab14-afc007d015ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019fcec5-a0e7-7340-b833-f7b32dfeefe5" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019fcec5-a0e7-7cce-ab14-afc007d015ab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fcec5-a0e7-71d0-a62e-b22d1b18b555" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019fcec5-a0e7-7cce-ab14-afc007d015ab" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fcec5-a0e7-71d0-a62e-b22d1b18b555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcec5-a0e7-71d0-a62e-b22d1b18b555_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fcec5-a0e7-71d0-a62e-b22d1b18b555" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcec5-a0e7-71d0-a62e-b22d1b18b555_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcec5-a0e7-7502-adeb-ca5065a154cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fcec5-a0e7-71d0-a62e-b22d1b18b555" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcec5-a0e7-7502-adeb-ca5065a154cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019fcec5-a0e7-705e-b483-185752ba35be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcec5-a0e7-7502-adeb-ca5065a154cf" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019fcec5-a0e7-705e-b483-185752ba35be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019fcec5-a0e7-7146-96ab-624c6384fc68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcec5-a0e7-7502-adeb-ca5065a154cf" xlink:to="loc_us-gaap_EmployeeStockMember_019fcec5-a0e7-7146-96ab-624c6384fc68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019fcec5-a0e7-7694-8511-244a4e31dd57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019fcec5-a0e7-7340-b833-f7b32dfeefe5" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019fcec5-a0e7-7694-8511-244a4e31dd57" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#TradingArrangmentsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllTradingArrangementsMember" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_AllTradingArrangementsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_OfficerTradingArrangementMember_01a18a19-ad2b-7fd6-bdb5-f3cc552e1c93" xlink:href="alab-20260930.xsd#alab_OfficerTradingArrangementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_alab_OfficerTradingArrangementMember_01a18a19-ad2b-7fd6-bdb5-f3cc552e1c93" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_GermaineCotaMember_01a05ab2-d534-7002-bbb8-74152368d7dc" xlink:href="alab-20260930.xsd#alab_GermaineCotaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_alab_GermaineCotaMember_01a05ab2-d534-7002-bbb8-74152368d7dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_JackLazarMember_019fcec5-a03e-7e96-aa1d-f7a99b266dc7" xlink:href="alab-20260930.xsd#alab_JackLazarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_alab_JackLazarMember_019fcec5-a03e-7e96-aa1d-f7a99b266dc7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alab_BethanyMayerMember_01a13aae-8753-7cdb-a77a-af6cb032867f" xlink:href="alab-20260930.xsd#alab_BethanyMayerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_alab_BethanyMayerMember_01a13aae-8753-7cdb-a77a-af6cb032867f" xlink:type="arc" order="4"/>
  </link:definitionLink>
</link:linkbase>
