The electrical properties of Ni-based ohmic contacts to N-face p-type GaN were investigated. The specific contact resistance of N-face p-GaN exhibits a linear decrease from 1.01 cm 2 to 9 05 × 10 −3 cm 2 for the as-deposited and the annealed Ni/Au contacts, respectively, with increasing annealing temperature. However, the specific contact resistance could be decreased down to 1 03× 10 −4 cm 2 by means of surface treatment using an alcohol-based (NH 4 2 S solution. The depth profile data measured from the intensity of O1s peak in the X-ray photoemission spectra showed that the alcohol-based (NH 4 2 S treatment was effective in removing the surface oxide layer of GaN