Spectroscopic ellipsometry (SE) together with the optical transmission method is successfully used to determine the refractive indexnand absorption coefficient &agr; of undoped gallium nitride film over the spectral range of 0.78–4.77 eV of photon energy. The SE measurement is carried out at angle of incidence of 60° over the 1.5–4.77 eV energy range and optical transmission measurement over the 0.78–3.55 eV energy range. The refractive indexnand absorption coefficient &agr; obtained by both methods show unique results in the overlap wavelength region. Refractive indexnis found to follow the Sellmeir dispersion relationshipn2(&lgr;)=2.272+304.72/(&lgr;2−294.02)below the fundamental band edge. A free excitonic structure at the band is clearly observed at room temperature, with the transmission energy of free exciton at 3.44 eV, which is in reasonable agreement with the reported results. ©1997 American Institute of Physics.