We report on the room temperature optical characterization of single crystal hexagonal GaN films on (0001) sapphire grown by metalorganic chemical vapor deposition. The energy gap of GaN was determined to be 3.400 eV by photoreflectance and the possible origin of the photoreflectance signal is discussed. Photocurrent measurement exhibited a peak at 3.351 eV and a continued photoresponse through the ultraviolet region. We found that the intensity of photocurrent was dependent upon the chopper frequency in the measurement. Absorption coefficient and film thickness were obtained from the optical transmission spectra. ©1995 American Institute of Physics.