We present a detailed study on the surface properties of conductive beta-Ga2O3 (1 0 0) single-crystal epiready substrates by means of photoelectron emission spectroscopy. The surface properties are studied prior and after annealing in ultra-high vacuum (UHV). We find that untreated substrates contain a significant amount of adsorbed carbon contaminations at the surface, which can be partly removed by annealing at 800 degrees C in UHV. Valence band photoemission evidences an upward band bending of about 0.5 eV that increases with annealing, revealing the presence of an electron depletion layer at the nearsurface region responsible for the insulating behavior commonly observed for semiconductive beta-Ga2O3 single crystals. Our findings become crucial for epitaxial growth, as it is known that carbon modifies the electrical and structural properties of subsequent epitaxial layers. (C) 2015 Elsevier B.V. All rights reserved.