A (Gd2O3)(1-x)(SiO2), (x = 0.5) gate dielectric film was deposited on an n-GaAs (0 0 1) substrate at various substrate temperatures. Bonding distribution of interfacial Ga and As was characterized by comparing the 3d and 3p photoelectron lines. Surface passivation using (NH4)(2)S was employed to preserve a stable interface. Interfacial GaAs oxide was not formed after the deposition, since bonding transition from As-S to Ga-S bonds provides thermal stability and protective effect against oxidation. While, without the passivation, interfacial GaAs-oxides were continuously grown as the substrate temperature was increased. The energy band gap of (Gd2O3)(0.5)(SiO2)(0.5) was defined as 6.8 eV using energy loss spectra of O 1s photoelectrons. The valence band maximum energy (E-VBM) of (Gd2O3)(0.5)(SiO2)(0.5) was determined to be 3.7 eV. By arrangement of the measured energy bandgap and E-VBM, the energy band structure of (Gd2O3)(0.5)(SiO2)(0.5)/GaAs system was demonstrated and an enhanced conduction band offset was observed. (C) 2004 Published by Elsevier B.V.