A numerical analysis to study the DX trap effects on the transient characteristics of the AlGaAs/GaAs HEMTs has been proposed. The Schrödinger and the Poisson equations are solved self-consistently to obtain the energy levels and the two-dimensional electron concentration in the GaAs quantum well. Both shallow and deep donors in the Si-doped AlGaAs are taken into account. A DX trap rate equation is employed in the numerical simulation of the drain current transient when a gate voltage pulse is applied. In our calculation, the two-region Grebene-Ghandhi model is utilized to show the transient IV characteristics of the devices. The simulation result indicates that the drain current has a significant transient response to a gate pulse in the micro-second range due to the DX centers. The overshoot current has a maximum value about 50% higher than the steady-state current at an aluminium mol fraction x ≈ 0.3. The influence of the gate pulse duty cycle on the magnitude of the overshoot has also been investigated.