GaN films were prepared by hot wall epitaxy on sapphire (0001) substrates from Ga and NH3sources. Growth characteristics of the GaN films were investigated from reflection high energy electron diffraction (RHEED) and x‐ray diffraction measurements, and effects of initial layers on the film growth are discussed. High quality films with streak RHEED patterns were obtained when the films were grown on a GaN initial layer prepared by Ga predeposition and its nitridation on surface nitrided sapphire substrates. ©1995 American Institute of Physics.