We　presented　980-nm　oxide-confined　vertical-cavity　surface-emitting　lasers　(VCSELs)　with　a　16-mu　m　oxide　aperture.　Optical　power,　voltage,　and　emission　wavelength　are　measured　in　an　ambient　temperature　range　of　5　degrees　C-80　degrees　C.　Measurements　combined　with　an　empirical　model　are　used　to　analyse　the　power　dissipation　in　the　device　and　the　physical　mechanism　contributing　to　the　thermal　rollover　phenomenon　in　VCSEL.　It　is　found　that　the　carrier　leakage　induced　self-heating　in　the　active　region　and　the　Joule　heating　caused　by　the　series　resistance　are　the　main　sources　of　power　dissipation.　In　addition,　carrier　leakage　induced　self-heating　increases　as　the　injection　current　increases,　resulting　in　a　rapid　decrease　of　the　internal　quantum　efficiency,　which　is　a　dominant　contribution　to　the　thermal　rollover　of　the　VCSEL　at　a　larger　current.　Our　study　provides　useful　guidelines　to　design　a　980-nm　oxide-confined　VCSEL　for　thermal　performance　enhancement.