ArF excimer laser photolysis of gas phase tetramethyltin was used to deposit thin organotin films on Si. In situ Auger electron spectroscopy and x-ray photoelectron spectroscopy (XPS) film analysis, showed the presence of C and Sn, which, according to C 1s and Sn 3d(5/2) peak deconvolution, were organized in highly branched polymeric chains Likely containing H as well. The film was oxidized at room temperature by exposure to controlled quantities of O-2 up to 5.4 x 10(12)L. Sn 3d(5/2), C 1s, and O 1s XPS peaks monitoring allowed us to follow the sequence of the oxidative reactions. It resulted that oxygen attacks first the Sn-H and Sn-C sites leading to the elimination of H2O and C containing volatile compounds, which determines a rearrangement of the cleaved bonds and an overall decrease of the measured C content. After this fast phase, oxygen is inserted in the Sn-Sn and Sn-C bonds, with formation of Sn-O-Sn, Sn-O-C, and Sn-C-O species. At the highest oxygen doses the dominating SnO2 component shows that almost all available Sn bonds are oxidized to Sn4+. However, either core level or valence-band spectroscopy demonstrated that below the near-surface layer the tin oxide phase remains substoichiometric, as if the SnO2 at the surface behaves as a passivating agent toward further oxidation.