By　using　scanning　electron　microscopy　(SEM)　and　infrared　data,　we　established　and　verified　a　two-dimensional　finite-element　model　conforming　to　the　size　of　the　practical　device　to　study　high-electron-mobility　transistors　(HEMTs).　Because　the　resolution　of　the　infrared　measurement　was　7　mu　m,　we　verified　the　correctness　of　the　model　by　comparing　the　7-mu　m　average　peak　temperature　with　the　measured　infrared　data　at　various　platform　temperatures.　The　simulated　average　peak　temperature　agrees　well　with　the　infrared　data.　To　further　investigate　the　thermal　performance　of　GaN-based　HEMTs　with　various　layer　sizes　and　structural　parameters,　we　simulated　devices　with　various　values　of　gate　length,　gate　spacing,　GaN　layer　thickness,　substrate　breadth,　and　substrate　thickness.　The　conclusions　presented　result　from　some　factors　that　must　be　taken　into　account　to　manage　thermal　issues　in　devices.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.