The Schottky-barrier formation of the Au/GaP (110) interface has been investigated by photoemission, in the presence of large surface photovoltage effects induced by the intense photon beam of a synchrotron-radiation source. The surface photovoltage has been measured with a Kelvin probe. The largest surface photovoltage shift observed in the photoemission spectra was almost 1 eV. The Schottky barrier appears to be fully established at about 8 Angstrom, while the surface photovoltage does not disappear until about 16 Angstrom. The Schottky-barrier height is 1.35+/-0.1 eV. The Kelvin-probe results demonstrate directly that the photoemission data must be corrected for the surface photovoltage during the formation of the barrier but are insensitive to it once full coverage is obtained. (C) 1996 American Vacuum Society.