Electron capture into insulator/silicon interface states is investigated for high-k dielectrics of Gd2O3 prepared by molecular beam epitaxy (MBE) and atomic layer deposition (ALD), and for HfO2 prepared by reactive sputtering, by measuring the frequency dependence of Metal Oxide Semiconductor (MOS) capacitance. The capture cross sections are found to be thermally activated and to increase steeply with the energy depth of the interface electron states. The methodology adopted is considered useful for increasing the understanding of high-k-oxide/silicon interfaces. (C) 2008 Elsevier Ltd. All rights reserved.