High quality gallium nitride thin films have been successfully grown on the Ga-diffused Si(111) substrates through ammoniating Ga2O3 thin films deposited by r.f. magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force microscope (AFM) and photoluminescence (PL) were used to characterize the synthesized samples. The analyses reveal that the formed films are high quality polycrystalline hexagonal gallium nitride. The as-formed GaN films show a flat surface topography with RMS roughness varied from 29 to 48 A. The strong near-band-edge-emission peak around 368 nm was observed at room temperature. This is a novel method to fabricate GaN thin films based on the direct reaction between Ga2O3 and NH3 on the Ga-diffused Si(111) substrates. (C) 2003 Elsevier Science B.V. All rights reserved.