We present a photoemission spectroscopy study of As-rich n-GaAs(001) surface modified by the deposition of an undoped silicon overlayer with thickness quite narrowly covering the interval from similar to 4 to 25 Angstrom. We observed a nonmonotonic relation between the surface band bending and Si overlayer thickness with the lowest surface potential at about 10-Angstrom-thick silicon overlayer. The valence band spectra inspection reveals the double leading edge incidental to alignment of the valence band edges of GaAs and Si overlayer with the offset of 0.29 eV and various theoretical models of semiconductor-semiconductor interfaces are discussed. Based on the influence of the silicon layer on both band bending and Schottky barrier height, it is concluded that the Schottky barrier height of Au/Si/GaAs structure evolves towards the Schottky limit for an ideal (par definition free of interface states) Au/GaAs junction as the silicon interlayer thickness reaches about 10 . (C) 2000 American Institute of Physics. [S0021-8979(00)04202-X].