We have employed the photoluminescence and x-ray photoelectron spectroscopy measurements to study the effects of (NH4)2Sx treatment on the p-type GaN (p-GaN). After (NH4)2Sx treatment, we found that the reduction of the surface state, related to nitrogen-vacancy defects on the p-GaN surface, led to a reduction in surface band bending by 0.25 eV. The surface band bending reduction and surface state reduction caused by the (NH4)2Sx surface treatment could be useful for the formation of ohmic and Schottky contacts between the metal and p-GaN layers. In addition, the intensity of the 2.8-eV photoluminescence band depended on the amount of nitrogen vacancy of p-GaN, which was also investigated in this study. © 2002 American Institute of Physics.