The　thermal　resistance　of　different　region　in　the　AlGaAs/GaAs　HEMTs　is　measured　in　a　large　temperature　range　by　the　pulsed　switching　electrical　method.　The　thermal　resistance　of　the　chip　solders　and　base　can　be　measured,　respectively,　through　the　cooling　response　curve　processed　by　the　structure　method.　As　the　temperature　increases,　the　total　thermal　resistance　increases　by　50%　from　-20　degrees　C　to　150　degrees　C.　And　the　increase　of　chip　thermal　resistance　is　about　67.2%　of　the　total　increased　thermal　resistance.　It　can　be　attributed　to　the　decrease　of　the　chip　heat　conductivity　and　the　enhancement　of　phonons　collisions.　The　result　is　significant　for　the　thermal　design　and　the　reliability　design　of　HEMTs.