A detailed simulation investigation is carried out on the hetero-structure complimentary (p+-p--p-n+) IMPATT oscillator for Terahertz power generation. It is observed that this newly proposed GaN/AlGaN IMPATT may generate a pulsed power density of ∼8×10 10 Wm-2 with an efficiency of 11%, whereas it's flatly doped counterpart is capable of delivering a pulsed power density of only 3×1010 Wm-2 with 7% efficiency. The total parasitic series resistance, RS, including that due to the un-depleted region in device and also the effects of ohmic contact resistances, has been found to be a major problem that reduces the negative resistance significantly and thus it has a detrimental effect on THz oscillation of the device. The study reveals that the value of RS decreases by 40% as the structure, semiconductor material pair as well as doping profile of the diode changes suitably from conventional to the proposed hetero-structure p+-p --p-n+ type, by incorporating a 300A0 Al 0.4Ga0.6N layer in the p-drift region. This first study will be a useful guide in the THz-sector to meet the ever-increasing demand of semiconductor THz-sources for application in Imaging or in improvised explosive device (IED) detection. © 2012 IEEE.