Molecular beam epitaxy deposited Ga2O3(Gd2O3) on Ge, without a commonly employed interfacial layer of GeON, has demonstrated excellent electrical properties, such as a high kappa value of 14.5, a low electrical leakage current density, and well behaved C-V characteristics even being subjected to 500 degrees C annealing in N-2 ambient for 5 min. In situ angle-resolved x-ray photoelectron spectroscopy (XPS) studies have revealed an abrupt Ga2O3(Gd2O3)/Ge interface without forming any interfacial layer. Further XPS studies explained the outstanding thermodynamic stability of the Ga2O3(Gd2O3)/Ge heterostructure. (C) 2008 American Vacuum Society.