The effects of self-heating and traps on the drain current transient responses of Al Ga N/Ga N HEMTs are studied by 2D numerical simulation. The variation of the drain current simulated by the drain turn-on pulses has been analyzed. Our results show that temperature is the main factor for the drain current lag. The time that the drain current takes to reach a steady state depends on the thermal time constant, which is 80 s in this case. The dynamics of the trapping of electron and channel electron density under drain turn-on pulse voltage are discussed in detail, which indicates that the accepter traps in the buffer are the major reason for the current collapse when the electric field significantly changes. The channel electron density has been shown to increase as the channel temperature rises. The effects of self-heating and traps on the drain current transient responses of Al Ga N / Ga N HEMTs are studied by 2D numerical simulation. The variation of the drain current simulated by the drain turn-on pulses has been analyzed. Our results show that temperature is the main factor for the drain current lag. The time that the drain current takes to reach a steady state depends on the thermal time constant, which is 80 s in this case. The dynamics of the trapping of electron and channel electron density under drain turn-on pulse voltage are discussed in detail, which indicates that the accepter traps in the buffer is the major reason for the current collapse when the electric field significant changes. The channel electron density has been shown to increase as the channel channel temperature rises .