The gallium oxide thin films with amorphous, crystalline, and nanostructure morphologies were deposited by a radio frequency magnetron sputtering system in ultra high vacuum conditions. High resolution X-ray photoelectron spectroscopy spectra of films were analyzed relating on the preparation conditions. On the amorphous films, the density of states at valence band region is dependent on the sputtering gas compositions. Beta gallium oxide (100) films are epitaxially deposited on magnesium oxide (100) crystalline substrate. The high resolution X-ray photoelectron spectra suggest the presence of the density of states valence band region with oxygen deficiency out of the stoichiometry on the epitaxial crystalline beta gallium oxide films. (C) 2007 Elsevier B.V. All rights reserved.