Gate-lag induced trapping effects due to donor-like surface traps located in the access regions between the electrodes of AlGaN/GaN HEMTs are investigated through TCAD transient simulations. The effects of variation in trap energy level and temperature on the current collapse transient characteristics have been studied. A simple physical model is proposed (based on the Arrhenius relation) to obtain the emission time constants versus trap energy level and temperature which is in a good agreement with TCAD simulations.