In　this　work,　we　presented　a　comprehensive　investigation　of　the　trapping　effect　in　the　GaN-based　high-electron-mobility　transistors　(HEMTs)　under　the　negative　gate-source　voltage　condition.　The　trapping　mechanisms　in　the　OFF　state　were　analyzed　and　the　trapping　behaviors　were　characterized　using　the　pulsed　measurements　preliminarily.　Specifically,　the　transient　drain-source　voltage　curves　under　a　certain　filling　condition　were　monitored　to　reflect　the　trapping　effect　in　the　OFF　state.　The　spectra　of　time　constant　and　differential　amplitude　were　combined　to　obtain　the　information　on　traps.　Three　traps　with　activation　energys　of　0.467,　0.552,　and　0.067　eV　were　characterized　using　the　transient　drain　voltage　curves　under　different　temperatures.　The　trap　characterization　methods　may　be　useful　for　the　further　study　of　the　trapping　behaviors　and　can　be　helpful　for　the　improvement　of　the　reliability　of　the　devices.　©　Published　under　licence　by　IOP　Publishing　Ltd.