A　convenient,　simple　method　is　proposed　to　measure　the　front　facet　temperature,　which　is　the　highest　temperature　in　the　semiconductor　laser　diode　(LD),　of　a　GaAs-based　laser　by　employing　thermoreflectance　technique.　Using　an　optical　system　featured　in　fiber　connection,　we　measured　the　facet　reflectivity　of　the　808-nm　AlGaInAs/AlGaAs　LD,　which　gives　information　about　the　temperature　of　the　output　facet.　The　fiber　system　operates　at　the　wavelength　of　1550　nm　which　avoids　the　absorption　of　the　probe　beam　by　the　tested　LD　and　consists　of　a　fiber-coupled　1550　nm　laser　illuminant　and　photodiode.　All　optical　elements　in　the　system　are　connected　by　the　fibers.　The　current　signal　collected　from　the　photodiode　is　related　to　the　facet　reflectivity　and　represents　facet　temperature.　We　compared　the　facet　temperatures　determined　by　thermoreflectance　technique　with　the　cavity　temperature　obtained　by　forward-voltage　method　and　found　that　the　former　is　as　much　as　three　times　as　the　latter.　©　2021　Institute　of　Physics　Publishing.　All　rights　reserved.