A gallium nitride (GaN) dual two - dimensional electron gas based high electron mobility transistor (D2DEGHEMT) is proposed and investigated based on TCAD simulations. According to the emulation, transfer characteristics curve and gate-source capacitance characteristic demonstrate that the GaN D2DEG-HEMT realizes normally-off feature with a threshold voltage of +4V. Besides, the off-state breakdown characteristics and Idrain-Vdrain output characteristics for the GaN D2DEG-HEMT and common GaN recessed gate MISHEMT (RG-MISHEMT) are also simulated. Results prove that the proposed GaN D2DEGHEMT has higher off-state breakdown voltage (465V, Lgd=2μm) and saturation current (above 1.5A/mm, Vgate=10V) comparing with the common GaN RG-MISHEMT under the same device size. Higher power density and wafer utilization are achieved in GaN D2DEG-HEMT.