Crystalline Y2O3 films on Si(111) were grown by ionized cluster beam (ICB) deposition in an ultra high vacuum (UHV). The crystallinity of the films deposited at several different temperatures was studied using X-ray diffraction (XRD) and reflection of high-energy electron diffraction (RHEED), and the chemical states of the films was investigated using X-ray photoelectron spectroscopy (XPS). The transformation from monoclinic to cubic structure was observed upon the increase of the substrate temperature from 100 degrees C to 500 degrees C. The single crystal cubic structure was obtained at substrate temperatures over 500 degrees C. The stoichiometry and binding state in the films were gradually changed to a cubic Y2O3 structure with the increase of the substrate temperature. The transformation of the film structure from a monoclinic structure to a cubic structure was also observed by post annealing treatment in an oxygen ambient.