<?xml version="1.0" encoding="utf-8"?>
<!--Generated by DFIN XBRL Instance Document - http://www.dfinsolutions.com/ - Version R3.0 - on 10-April-2025 [02:52:50] {PM}-->
<schema targetNamespace="http://www.SixthStreetSpecialtyLending.com/20250522" elementFormDefault="qualified" xmlns:tslx="http://www.SixthStreetSpecialtyLending.com/20250522" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xl="http://www.xbrl.org/2003/XLink" xmlns:us-gaap="http://fasb.org/us-gaap/2024" xmlns:country="http://xbrl.sec.gov/country/2024" xmlns:currency="http://xbrl.sec.gov/currency/2024" xmlns:dei="http://xbrl.sec.gov/dei/2024" xmlns:exch="http://xbrl.sec.gov/exch/2024" xmlns:naics="http://xbrl.sec.gov/naics/2024" xmlns:sic="http://xbrl.sec.gov/sic/2024" xmlns:us-types="http://fasb.org/us-types/2024" xmlns:stpr="http://xbrl.sec.gov/stpr/2024" xmlns:deprecated="http://www.xbrl.org/2009/arcrole/fact-explanatoryFact" xmlns:srt="http://fasb.org/srt/2024" xmlns:srt-types="http://fasb.org/srt-types/2024" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2020-01-21" xmlns:cef="http://xbrl.sec.gov/cef/2024" xmlns:cef-pre="http://xbrl.sec.gov/cef-pre/2024">
<annotation>
<appinfo>
<link:roleType roleURI="http://www.SixthStreetSpecialtyLending.com/role/N2SharePriceTable" id="N2SharePriceTable">
<link:definition>1001 - Disclosure - N-2 - [Share Price Table]</link:definition>
<link:usedOn>link:presentationLink</link:usedOn>
<link:usedOn>link:definitionLink</link:usedOn>
<link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
</appinfo>
</annotation>
<import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
<import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" />
<import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" />
<import namespace="http://xbrl.sec.gov/dei/2024" schemaLocation="https://xbrl.sec.gov/dei/2024/dei-2024.xsd" />
<import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd" />
<import namespace="http://xbrl.sec.gov/cef/2024" schemaLocation="https://xbrl.sec.gov/cef/2024/cef-2024.xsd" />
<import namespace="http://xbrl.sec.gov/cef-pre/2024" schemaLocation="https://xbrl.sec.gov/cef/2024/cef-2024_pre.xsd" />
</schema>
