Our ability of controlling the growth and interfaces of thin dielectric films on III-V semiconductors by ultrahigh vacuum deposition has led to investigations of gate stacks containing rare earth oxides of Gd2O3 and Y2O3 as alternative high K gate dielectrics for Si. The abrupt interfaces achieved in these gate stacks have enabled the electrical, chemical, and structural studies to elucidate the critical materials integration issues for CMOS scaling, including morphology dependence, interfacial structure and reaction, thermal stability and gate electrode compatibility. (C) 2002 Elsevier Science B.V. All rights reserved.