<?xml version="1.0" encoding="utf-8"?>
<!--XBRL document created with Toppan Merrill Bridge  11.3.0.1 -->
<!--Based on XBRL 2.1-->
<!--Created on: 5/19/2026 12:57:07 PM-->
<!--Modified on: 5/19/2026 12:57:07 PM-->
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  <xsd:annotation>
    <xsd:appinfo>
      <link:roleType roleURI="http://golubcapitalbdc.com/role/DocumentDocumentAndEntityInformation" id="DocumentDocumentAndEntityInformation">
        <link:definition>995200090 - Document - Document and Entity Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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  <xsd:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
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  <xsd:element name="SubscriptionRightsMember" id="gbdc_SubscriptionRightsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="WarrantsMember" id="gbdc_WarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
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  <xsd:element name="TrsMember" id="gbdc_TrsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
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  <xsd:element name="Gcic2018DebtSecuritizationMember" id="gbdc_Gcic2018DebtSecuritizationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
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  <xsd:element name="CreditFacilityMember" id="gbdc_CreditFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="MsCreditFacilityMember" id="gbdc_MsCreditFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="MsCreditFacilityIiMember" id="gbdc_MsCreditFacilityIiMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
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  <xsd:element name="AdviserRevolverMember" id="gbdc_AdviserRevolverMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="SbaDebenturesMember" id="gbdc_SbaDebenturesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
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  <xsd:element name="Notes2027Member" id="gbdc_Notes2027Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="NotesWillBeUnsecuredAndThereforeWillBeEffectivelySubordinatedToAnySecuredIndebtednessCurrentlyIncurredOrMayIncurInFutureMember" id="gbdc_NotesWillBeUnsecuredAndThereforeWillBeEffectivelySubordinatedToAnySecuredIndebtednessCurrentlyIncurredOrMayIncurInFutureMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="NotesWillBeStructurallySubordinatedToIndebtednessAndOtherLiabilitiesOfSubsidiariesMember" id="gbdc_NotesWillBeStructurallySubordinatedToIndebtednessAndOtherLiabilitiesOfSubsidiariesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="IndentureGoverningNotesWillContainLimitedProtectionForHoldersOfNotesMember" id="gbdc_IndentureGoverningNotesWillContainLimitedProtectionForHoldersOfNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="DefaultOnObligationsToPayOtherIndebtednessMayNotBeAbleToMakePaymentsOnNotesMember" id="gbdc_DefaultOnObligationsToPayOtherIndebtednessMayNotBeAbleToMakePaymentsOnNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="DowngradeOrWithdrawalOfRatingAssignedByRatingAgencyToNotesMember" id="gbdc_DowngradeOrWithdrawalOfRatingAssignedByRatingAgencyToNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="IncreaseInMarketInterestRatesResultsInMarketValueOfNotesMember" id="gbdc_IncreaseInMarketInterestRatesResultsInMarketValueOfNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="OptionalRedemptionProvisionAffectReturnOnNotesMember" id="gbdc_OptionalRedemptionProvisionAffectReturnOnNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="MayNotBeAbleToRepurchaseNotesUponChangeOfControlRepurchaseEventMember" id="gbdc_MayNotBeAbleToRepurchaseNotesUponChangeOfControlRepurchaseEventMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="DebtOutstandingIncreaseAffectPaymentObligationsUnderNotesAndOtherDebtMember" id="gbdc_DebtOutstandingIncreaseAffectPaymentObligationsUnderNotesAndOtherDebtMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="ActiveTradingMarketForNotesNotAbleToResellMember" id="gbdc_ActiveTradingMarketForNotesNotAbleToResellMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="Gbdc32021DebtSecuritizationMember" id="gbdc_Gbdc32021DebtSecuritizationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="Gbdc32022DebtSecuritizationMember" id="gbdc_Gbdc32022DebtSecuritizationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="Gbdc3DbCreditFacilityMember" id="gbdc_Gbdc3DbCreditFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="Gbdc320222DebtSecuritizationMember" id="gbdc_Gbdc320222DebtSecuritizationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="Notes2029Member" id="gbdc_Notes2029Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="ExistingNotesMember" id="gbdc_ExistingNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="Debt2024SecuritizationMember" id="gbdc_Debt2024SecuritizationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
</xsd:schema>
