We report on the effect of Ni and NiO interlayers on an indium oxide-doped ZnO (IZO)-based ohmic scheme for a transparent and low resistance contact to the p-GaN. Ni/IZO and NiO/IZO contact layers on p-GaN yielded very low specific contact resistances of 9.2 × 10-5 and 3.6 × 10 -5 Ω cm2, respectively, after annealing at 500°C for 1 min under a nitrogen ambient. Auger electron spectroscopy and X-ray photoemission spectroscopy analysis of the IZO and p-GaN interface indicated that Ga atoms out-diffused and the NiO phase was formed at the interface region after the thermal annealing process, resulting in a decrease in contact resistance. © 2005 The Electrochemical Society. All rights reserved.