Photocatalytic　oxidation　of　benzene　to　phenol　using　molecular　O2　is　one　of　the　most　promising　sustainable　approaches　for　the　green　synthesis　of　phenol.　Introducing　oxygen　vacancies　(OVs)　on　semiconductor　surfaces　by　defect　engineering　is　a　promising　strategy　to　enhance　the　efficiency　of　benzene　oxidation　to　produce　phenol　due　to　the　unique　functions　of　OVs　in　facilitating　the　charge　separation　and　activation　of　molecular　O2.　Herein,　a　vacuum-sealed　annealing　strategy　has　been　well　developed　to　generate　abundant　surface　OVs　on　semiconductors,　such　as　WO3.　The　well-sealed　quartz　vial　creates　a　well-controlled　low-pressure　condition　for　the　formation　of　OVs　without　the　need　for　external　energy　for　maintaining　the　vacuum　state.　Moreover,　the　gaseous　species　generated　during　the　thermal　annealing　process　help　mitigate　stress-induced　defects,　particularly　bulk　defects.　The　vacuum-sealed　annealed　WO3　with　sufficient　OVs　and　reduced　bulk　defects　shows　a　better　photocatalytic　performance　in　the　one-step　oxidation　of　benzene　to　phenol　with　O2,　compared　to　the　WO3　synthesized　through　thermal　annealing　in　Ar　and　H2　atmospheres.　The　present　vacuum-sealed　annealing　strategy　is　found　to　be　further　applicable　to　engineer　a　wide　range　of　semiconducting　photocatalysts　with　abundant　OVs　to　optimize　their　properties　for　efficient　photocatalysis　and　other　OV-promoted　systems.　©　2025　American　Chemical　Society.