Cleaved GaAs surface under ultra high vacuum was analyzed using X-ray photoelectron spectroscopy. Sulfidation-treated GaAs surface resulted in the formation of S-Ga, O-Ga, S-As, and O-As bonds. For characterizing the suface treated GaAs, the cleaved sample was used as a controlled sample. The evolution of Ga 2p3 and 3d peaks in the cleaved, HCI-treated, and sulfidation-treated GaAs were monitored with exposing time to the air. After exposure for 10 days, the oxidation of GaAs surface seemed to be almost saturated. With the sulfidation treated sample, the increases of Ga-O and As-O bonds resulted from the decomposition of sulfur bonds. The exchang of sulfur with Oxygen bonds was in good accordance with the results obtained from the sample exposed in the air.