High quality GaN films were prepared by annealing sputtered Ga2O3 films under flowing ammonia. Ga2O3 films were deposited on Si (1 1 1) substrates by r.f. magnetron sputtering. X-ray diffractorneter (XRD) and X-ray photoelectron spectroscopy (XPS) measurement results indicate that the polycrystalline GaN with hexagonal structure was successfully grown on, the Si (1 1 1) substrate. The surface morphology of the GaN films was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Varying the annealing temperature and time was found to have great effect on the grain size. (C) 2002 Elsevier Science B.V. All rights reserved.