LiNbO3 thin films were grown by rf magnetron sputtering on (0001)-GaN templates and AlGaN/GaN structures. The films were characterized by four-circle x-ray diffraction, atomic force microscopy (AFM), and transmission electron microscopy (TEM). No second phases, such as a Li-excess or Li-deficient phase,. were detected by theta-2theta scans and the films were highly (0001) textured. LiNbO3 {2024} phi-scans and the electron diffraction pattern show that the films were epitaxially grown on GaN with crystallographic registry. The LiNbO3 c-plane was parallel to the c-plane of the GaN, but there was a 30degrees in-plane rotation between the LiNbO3 and GaN so that [1100](LiNbO3) parallel to [1120](GaN(AlGaN)) and the LiNbO3 films had two variants of grains rotated 60degrees in-plane to each other. It was confirmed by high resolution TEM that there was a transition layer between LiNbO3 and GaN. The films were annealed to improve the crystallinity and following annealing investigated using convergent beam electron diffraction (CBED) to determine the polarity. The films grow with a spontaneous polarization vector opposite to that of the underlying GaN film. (C) 2005 American Vacuum Society.