Gallium nitride (GaN) films have been successfully fabricated on silicon (111) substrates through ammoniating Ga2O3/Al2O3 films deposited by rf magnetron sputtering. The formed films were characterized by Fourier transform infrared (FTIR) transmission spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) , scanning electron microscopy (SEM) and photoluminescence spectrum(PL). The results indicate that the films formed are polycrystalline GaN with hexagonal wurtzite structure.