The series of gas sensors based on SnO2 thin films and doped with different amount of Cu was prepared by using de magnetron sputtering. The surface properties and chemical composition of the sensors covered with Cu and Pt overlayers were studied by XPS, SIMS and optical UV-VIS spectroscopy. The electrical conductivity controlled by surface interaction with gases (CO, H-2, Cl-2) was also investigated experimentally. Obtained depth profiles demonstrate that the surface doping with Cu results in nearly uniform Cu distribution through the whole thickness of the SnO2, film, while the Pt-doping modifies only the surface of the sample, The origin of different Cu and Pt distributions in depth and their influence to the surface chemical reactions during gas treatments are discussed. The chemical stale of Cu-dopant and its effect to the Valence band (XPS) and optical (W-VIS) spectra are analysed.