Electron energy barriers at the interfaces of GaAs(100) with Gd2O3 appear to be insensitive to the Fermi level pinning indicating that charges at interface states are of marginal importance for the band alignment at semiconductor/insulator interfaces. The inferred conduction band offset of 1.6 +/- 0.1 eV for GaAs(100)/Gd2O3 is close to that measured at the GaAs(100)/LaAlO3 interface which is consistent with the 5.8 and 5.7 eV wide band gaps of these two insulators. However, the defects revealed by photoionization measurements exhibit a distinctly different in-depth distribution. In GaAs/LaAlO3 most of the traps are located close to the semiconductor surface, while in GaAs/Gd2O3 case they are found distributed across the entire oxide layer. (c) 2006 American Institute of Physics.