The　self-heating　effect　on　the　drain　current　transient　response　in　AlGaN/GaN　high　electron　mobility　transistors　(HEMTs)　was　investigated　experimentally.　Two　steps　were　observed　as　the　drain　current　dropped　with　time.　The　relationship　between　the　transient　temperature　rise　in　the　channel　and　the　drop　in　the　drain　current　are　discussed　in　detail.　The　decrease　in　the　transient　drain　current　and　the　rise　in　the　channel　transient　temperature　had　a　complementary　relationship.　The　decrease　in　the　channel　electron　mobility,　caused　by　self-heating,　was　an　important　factor　in　the　drain　current　drop　in　the　AlGaN/GaN　HEMTs.