In　this　paper　thermal　characteristic　and　front　facet　of　the　808　nm　GaAs-Based　laser　diodes　(LDs)　before　and　after　degradation　are　presented　and　discussed.　The　relation　between　thermal　characteristic　and　the　change　of　facet　is　analyzed.　Aging　tests　are　carried　out　under　the　conditions　of　the　constant　current　stress　(3　A),　and　the　junction　temperature　of　LD　is　fixed　at　70　°C.　The　total　thermal　resistance　increases　from　2.9　to　6.5　°C/W　before　and　after　degradation.　Furthermore,　the　contribution　of　each　component　to　the　total　thermal　resistance　has　been　obtained　from　the　differential　structure　function　and　cumulative　structure　function.　The　thermal　resistance　of　chip　becomes　slightly　larger　in　magnitude　after　degradation　than　that　before　degradation,　while　significant　increase　in　the　thermal　resistance　of　solder　layer　(indium　attaching　material)　and　package　body　is　observed　after　degradation.　In　addition,　some　spots　and　lines　of　melted　materials　are　observed　using　laser　microscope　after　degradation,　which　lead　to　temperature　increase　of　front　facet　and　the　optical　power　decrease.　We　can　see　that　the　total　thermal　resistance　increase　with　the　appearance　of　these　spots　and　lines　defect　in　facet　of　LDs.　Consequently,　from　the　results　above　we　can　conclude　that　the　performance　of　LDs　could　be　improved　through　optimizing　of　the　front　facet　and　package　body　of　LDs.　©　2011　IEEE.