Blue　GaN-based　laser　diodes　(LDs)　have　been　characterized　by　thermal　infrared　imaging　and　transient　thermal　technique　to　obtain　temperature　distributions　along　the　optical　resonant　cavity　under　continuous-wave　(CW)　operation.　The　highest　temperature　occurred　at　the　emitting　facet　and　the　second　higher　temperature　occurred　in　the　other　reflecting　facet　under　injection　current　I　=　100　mA　with　platform　temperature　of　308.15　K.　The　results　are　attributed　to　the　nonradiative　recombination　in　the　active　region　and　the　reabsorption　of　laser　light　inside　the　cavity.　And　due　to　the　different　of　optical　flow　density,　the　highest　temperature　appears　in　emitting　facet.　Based　on　diode　forward　voltage　with　temperature,　transient　thermal　technique　is　used　to　obtain　the　temperature　distribution　along　the　top-down　direction　of　LDs　by　the　structure　function　method.　The　thermal　resistance　from　chip　to　case　is　47.3　K/W.　The　chip＇s　thermal　resistance　is　the　main　contribution.　©　2015　Elsevier　Ltd.　All　rights　reserved.