The　reliability　of　GaN-based　high　electron　mobility　transistors　(HEMTs)　is　of　great　importance　due　to　the　special　characteristics　of　AlGaN/GaN　heterostructure　such　as　intense　polarization　effect,　high　material　defect　density,　strong　electric　field　working　condition,　complicated　process　etc.　Failure　analysis　is　the　premise　and　foundation　to　improve　reliability　of　semiconductor　devices.　However,　there　is　less　research　on　failure　analysis　method　about　HEMTs　at　present.　In　this　paper,　an　effective　method　of　failure　analysis　of　HEMT　is　presented　to　analyze　the　failure　reason　of　electrical　stress　on　many　occasions,　and　a　corresponding　case　analysis　of　HEMT　is　carried　out.　Following　the　unique　complementary　detection　process　of　electrical　testing,　thermal　radiation　and　photon　emission,　device　failure　position　can　be　determined　rapidly　and　failure　mode　and　mechanism　can　be　analyzed　by　this　method.　A　4-finger　GaN-based　HEMT　with　a　operating　voltage　of　28V　and　a　gate　width　of　1.25mm　are　analyzed　according　to　this　failure　analysis　method.　Two　failure　positions　were　localized　and　the　failure　mode　and　mechanism　were　determined　by　comprehensive　analysis　of　testing　images　and　data.　Finally,　several　improvements　in　design　and　process　of　GaN-based　HEMTs　are　proposed,　which　is　a　valuable　reference　on　the　failure　analysis　and　reliability　enhancement　of　HEMT　devices.