The　reliability　of　GaN　high-electron-mobility　transistors　remains　limited　by　trapping,　and　a　new　way　to　characterize　traps　is　through　the　drain　current　transient.　In　this　paper,　we　report　a　differential　amplitude　spectrum　(DAS)　from　which　we　could　extract　the　exact　amount　that　a　trap　contributes　to　charging/discharging　from　the　current　transient.　We　compared　the　time　constant　spectrum　and　the　DAS　in　extracting　traps＇　amplitudes　theoretically　and　experimentally.　Using　the　DAS,　we　investigated　the　trapping　effect　and　systematically　identified　the　positions　and　mechanisms　of　traps　with　Ea　values　of　0.10,　0.38,　0.45,　and　0.61　eV　in　our　samples.　In　particular,　we　demonstrated　that　the　semi-oN　state　with　high-drain　voltage　in　the　filling　process　can　maximize　the　charge　trapping　in　both　the　AIGaN　layer　and　GaN　buffer.　In　addition,　we　experimentally　proved　that　measured　voltage　in　the　linear　region　was　the　best　choice　for　these　samples.