Abstract: Gallium nitride thin films have been successfully grown on the Ga-diffused Si (111) substrates through nitriding Ga₂O₃ thin films deposited by r.f. magnetron sputtering and the growth condition was investigated. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were employed to analyze the structure and surface morphology of the synthesized samples. The results reveal that the as-grown films are hexagonal GaN. Varying the Ga-diffused time and the mitriding time were found to have great effect on the crystal quality of GaN films, and the crystal quality and the thin film quality were improved with the increasing Ga-diffused time. And a small change have taken on the pellet shape of the GaN thin film with the increasing nitriding time.