A　novel　method　to　realize　single-transverse-mode　emission　by　incorporating　a　built-in　index　guide　is　employed　on　vertical-cavity　surface-emitting　lasers　(VCSELs)　with　a　large　oxide　aperture.　The　etched　index　guide　provides　modal　loss　discrimination　for　mode　selection　and　transverse　optical　field　confinement　for　light　propagating　in　the　longitudinal　direction.　A　single-transverse-mode　VCSEL　with　side-mode　suppression　ratio　＞30　dB　under　the　full　range　of　bias　currents　is　achieved.　The　thermal　resistance　of　the　device　is　lower　than　one　half　of　the　counterpart　of　the　conventional　GaAs-based　single-mode　VCSELs.　Moreover,　compared　with　an　ordinary　VCSEL　with　the　same　oxide　aperture　diameter,　the　beam　quality　of　the　device　incorporated　a　built-in　index　guide　has　been　significantly　improved.　The　divergence　angle　of　the　output　beam　estimated　from　the　full-width-half-maximum　of　the　far-field　pattern　is　as　small　as　9　degrees.