The potential impact of gallium-nitride (GaN) high electron mobility transistor (HEMT) with a p-layer in the barrier is reported. We investigate the device performance focusing on short channel effects, gate–drain capacitance, electric field, breakdown voltage, DC output conductance (go), drain current, DC trans-conductance (gm) and sub-threshold slope using two-dimensional and two-carrier device simulations. Our simulation results reveal that the proposed structure reduces the short channel effects, gate–drain capacitance, sub-threshold slope and go compared to the conventional and T-gate structures. Also this new structure reduces the peak electric field at the gate corner near the drain and consequently increases the breakdown voltage significantly. Increasing p-layer length (Lp) and thickness (Tp), improves the breakdown voltage, short channel effects, gate–drain capacitance and go.