Band alignment of Gd2O3 gate oxide films on n-GaAs(0 0 1) was controlled by the incorporation Of SiO2. The photoelectron binding energy shifts in Gd2SiO5 film could be interpreted with relative electronegativity of second nearest neighbor element. The surface and interface morphology of Gd2SiO5/n-GaAs structure was smooth due to the absence of crystalline phase. Energy band gaps were estimated as similar to 5.8 and 6.6 eV for Gd2O3 and Gd2SiO5, respectively, by combining photoemission with absorption spectra. A decrease of leakage current density and a saturated accumulation capacitance indicate an enhanced band offset and small roughness in Gd2SiO5/n-GaAs system. (c) 2004 Published by Elsevier B.V.