We present the surface analysis of (NH4)2Sx-treated InGaN using x-ray photoelectron spectroscopy. The native oxide and organic contamination on the InGaN surface can be removed by (NH4)2Sx surface treatment. However, the hydroxyl species present on the InGaN surface cannot be removed. Because Ga–S and In–S bonds were formed and N–S bonds were not observed, we deduce that the sulfur atoms would occupy the nitrogen-related vacancies and bond with the Ga and In atoms. The clean surface and surface state reduction caused from the (NH4)2Sx surface treatment would be useful for the formation of ohmic and Schottky contacts between the metal and InGaN layers. © 2001 American Vacuum Society.