Formation of ultrathin oxide layer in water-based processes, resulting in hydroxyl group termination, is an essential process technology for high-k dielectric stack formation with atomic layer chemical vapor deposition (ALCVD) layers. A silicon(100) surface treated in water vapor in the temperature range of typical ALCVD processes has been studied by high-resolution X-ray photoelectron spectroscopy (HRXPS) analysis. HF-last cleaned silicon (100) surface is stable in water vapor up to 300 degrees C. From 350 degrees C, the surface undergoes significant change in bonding configurations. HRXPS showed that a 6 Angstrom thick oxide was grown in water vapor at 350 and 400 degrees C. The HRXPS analysis also showed that the intensity of the left shoulder of the bulk silicon peak in XPS Si 2p spectra is related to the hydrogenated silicon atoms (Si-H). Quantification of the Si-H peak demonstrated that the oxidation is related to the hydrogen desorption on the surface. It has been proposed that the hydrogen desorption is the limiting step in the oxidation process water vapor.