The room temperature optical properties of single crystal hexagonal GaN films on (0001) sapphire grown by metalorganic chemical vapor deposition are reported in this article. The energy gap of hexagonal GaN was determined as 3.39 and 3.400 eV by optical transmission and photoreflectance (PR), respectively, and refractive index of GaN film as the function of photon energy was obtained. The possible origin of the PR signal was attributed to the modulation of the surface field and line shape broadening of defects. Raman scattering spectra were employed to investigate the photon modes of the GaN film. The properties of longitudinal optical phonon-plasmon coupled modes were further studied, and the carrier concentration and damping constant were determined by line-shape fitting of the coupled modes.