In　this　article,　a　trap　characterization　system　based　on　the　transient　drain　voltage　was　constructed　to　achieve　the　complete　measurement　and　analysis　of　traps　in　GaN　high-electron-mobility　transistors　(HEMTs).　Through　the　appropriate　design　of　the　measurement　circuit　and　acquisition　system,　the　transient　drain　voltage　variations　caused　by　trapping　behaviors　in　the　GaN　HEMTs　can　be　obtained.　A　time　constant　extraction　method　based　on　the　Bayesian　deconvolution　function　was　used　to　optimize　the　trap　extraction　accuracy,　and　the　trap　properties,　including　time　constant,　absolute　amplitudes,　and　energy　levels,　can　be　comprehensively　characterized.　In　combination　with　the　above　trap　features,　the　response　of　trapping　behaviors　to　various　bias　voltages　was　obtained　to　analyze　the　trap　positions.　With　respect　to　the　GaN　HEMTs　with　different　processes　and　fabrications,　extensive　measurements　of　energy　levels　were　performed　on　four　kinds　of　samples　to　confirm　the　validity　of　the　proposed　characterization　system,　and　four　devices　of　each　kind　were　used　to　verify　the　repeatability　of　experimental　results.　It　indicated　that　the　constructed　instrument　and　measurement　methods　can　realize　the　accurate　and　nondestructive　characterization　of　traps.　The　method　used　in　this　study　can　be　potentially　beneficial　to　better　understand　the　reliability　issues　and　optimize　the　performance　of　devices.