We have investigated the properties of cleaved SmB6 single crystals by x-ray photoelectron spectroscopy. At low temperatures and freshly cleaved samples a surface core level shift is observed which vanishes when the temperature is increased. A Sm valence between 2.5 and 2.6 is derived from the relative intensities of the Sm2+ and Sm3+ multiplets. The B/Sm intensity ratio obtained from the core levels is always larger than the stoichiometric value. Possible reasons for this deviation are discussed. The B 1s signal shows an unexpected complexity: An anomalous low energy component appears with increasing temperature and is assigned to the formation of a suboxide at the surface. While several interesting intrinsic and extrinsic properties of the SmB6 surface are elucidated in this manuscript, no clear indication of a trivial mechanism for the prominent surface conductivity is found.