The structure of GaN films grown by hydride vapor phase epitaxy on sapphire substrates has been studied by x-ray diffraction, transmission electron microscopy (TEM), and atomic force microscopy. Films, 15–80 &mgr;m thick, were grown onc-plane sapphire that were either pretreated with GaCl or contained a ZnO sputter deposited layer. The defect density, for both types of films, was found by plan view TEM to range between mid-107to mid-108 dislocations/cm2despite very different structural defects at the film/substrate interface. Nanovoids were found; however, no cracks were observed in the films that were investigated by TEM. ©1997 American Institute of Physics.