This work reports on the X-ray photoemission spectroscopy (XPS) measurements of the As-rich GaAs(001) surface properties developing due to the different thicknesses of the undoped silicon overlayers. We analyzed the bond nature on the silicon-GaAs interface depending on the silicon thickness which was connected with observed variations in surface Fermi level positions. Further, the Au/Si/n-GaAs metal-semiconductor contacts were prepared on the studied structures. Measured changes in the Schottky barrier height for silicon thicknesses till approximately I nm are interpreted through the approach of the Schottky barrier height to Schottky limit due to decrease of the interface state densities on the Si/GaAs interface. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.