Germanium technology aiming at the fabrication of functional devices strongly depends on the electrical behaviour of both the oxide bulk and the oxide/Ge interface. Field effect transistors underperform and express non ideal characteristics due to high values of interface defects in conjunction with bulk states. In this paper, we show that rare earth oxide layers of Gd2O3 prepared by molecular beam deposition on Ge substrates produce improved insulating characteristics. The current density at I V was as low as J = 50 nA/cm(2). The calculated value of the dielectric constant was around 10 and an EOT value equal to 3.7 nm was obtained, while the density of the interface states was approximately 2 x 1012 cm(-2) eV(-1). A detailed analysis of the electrical measurements of MOS capacitors revealed the existence of bulk electron traps in the semiconductor which need special attention if rare earth oxides are to be used in Ge based MOS devices. (c) 2006 Elsevier Ltd. All rights reserved.