Surface properties of wet-cleaned or successively passivated GaAs with (NH4)(2)S-x solution were analyzed using x-ray photoelectron spectroscopy. All the treatments were carried out in a glove box under nitrogen controlled atmosphere. Every cleaning process with HCl or H3PO4 solution produced elemental As and the amount depends on the etching capability of acid to GaAs. Successive sulfidation treatment resulted in the formation of an As-S bond, and the observed quantity of the arsenic sulfide was closely related to the amount of elemental As. In particular, the As-S was hardly observed in the sulfidation treated GaAs surface after NH4OH treatment because elemental As had not been produced by the NH4OH treatment. The in situ annealed GaAs surface at 600 degrees C contained a large amount of elemental Ga and showed an effective formation of Ga-S after the sulfidation treatment. Therefore, it could be assured that the elemental forms of As and Ga bind with S through the sulfidation treatment using a (NH4)(2)S-x solution.