The　evaluation　of　thermal　resistance　constitution　for　packaged　AlGaN/GaN　high　electron　mobility　transistor　(HEMT)　by　structure　function　method　is　proposed　in　this　paper.　The　evaluation　is　based　on　the　transient　heating　measurement　of　the　AlGaN/GaN　HEMT　by　pulsed　electrical　temperature　sensitive　parameter　method.　The　extracted　chip-level　and　package-level　thermal　resistances　of　the　packaged　multi-finger　AlGaN/GaN　HEMT　with　400-mu　m　SiC　substrate　are　22.5　K/W　and　7.2　K/W　respectively,　which　provides　a　non-invasive　method　to　evaluate　the　chip-level　thermal　resistance　of　packaged　AlGaN/GaN　HEMTs.　It　is　also　experimentally　proved　that　the　extraction　of　the　chip-level　thermal　resistance　by　this　proposed　method　is　not　influenced　by　package　form　of　the　tested　device　and　temperature　boundary　condition　of　measurement　stage.