In this paper, two-dimensional(2D) transient simulations of an Al Ga N/Ga N high-electron-mobility transistor(HEMT)are carried out and analyzed to investigate the current collapse due to trapping effects. The coupling effect of the trapping and thermal effects are taken into account in our simulation. The turn-on pulse gate-lag transient responses with different quiescent biases are obtained, and the pulsed current–voltage(I–V) curves are extracted from the transients. The experimental results of both gate-lag transient current and pulsed I–V curves are reproduced by the simulation, and the current collapse due to the trapping effect is explained from the view of physics based on the simulation results. In addition, the results show that bulk acceptor traps can influence the gate-lag transient characteristics of Al Ga N/Ga N HEMTs besides surface traps and that the thermal effect can accelerate the emission of captured electrons for traps. Pulse transient simulation is meaningful in analyzing the mechanism of dynamic current collapse, and the work in this paper will benefit the reliability study and model development of Ga N-based devices. In this paper, two-dimensional (2D) transient simulations of an Al Ga N / Ga N high-electron-mobility transistor (HEMT) are carried out investigate the current collapse due to trapping effects. and thermal effects are taken into account in our simulation. The turn-on pulse gate-lag transient responses with different quiescent biases are obtained, and the pulsed current-voltage (I-V) curves are extracted from the transients. The experimental results of both gate-lag transient current and pulsed I-V curves are reproduced by the simulation, and the current collapse due to the trapping effect is explained from the view of physics based on the simulation results. In addition, the results show that bulk acceptor traps can influence the gate-lag transient characteristics of Al Ga N / Ga N HEMTs besides surface traps and that the thermal effect can accelerate the emission of captured electrons for traps. in analyzing the mechanism of dynamic current collapse, and the work in this paper will benefit the reliability study and model development of Ga N-based devices.