Optical processes at the absorption edge in Y‐doped BaCeO3films with thicknesses of 160 and 4600 nm have been studied in the temperature region between 20 and 1000 °C. For the first time, optical band‐gap energies of Y‐doped BaCeO3were determined with a room temperature value of 4.1 eV and a temperature coefficient of −3.88×10−4eV/K. It was found that the optical absorption coefficient below the band–band transition exhibits an exponential dependence on photon energy following Urbach’s rule, and the Urbach tail is dependent on oxygen partial pressures, i.e., on lattice defects. The corresponding Urbach edge parameters and their temperature dependence were investigated. The data are discussed within the model of structural and thermal disorder and a characteristic phonon energy of 46 meV was obtained according to this disorder model. ©1996 American Institute of Physics.