Semiconducting thin films were obtained from a mixture of Ar + TMT (tetramethyltin) + O2 in an r.f. glow discharge diode reactor at low pressure (10-100 Pa). Different substrates were used : glass, quartz, polymer (PP, PE) silicon and SiO2. Emission spectroscopy was employed to estimate the energetic character of the discharge and to characterize the excited species in the plasma phase. Different surface diagnostic techniques (profilometry, X-ray photoelectron spectroscopy (XPS), Fourier transform IR (FTIR), scanning electron microscopy (SEM), four-point probe measurements, optical transmission) reveal the formation of carbon-free non-stoichiometric tin oxide films with perfectly controlled conductivities varying from 10(-4) up to 10(2) S cm-1. The films examined by interface capacity measurements were n type semiconductors with a carrier concentration ranging between 10(15) and 10(17) cm-3 and a band gap measured by optical transmission varying between 3.5 and 4 eV. The conductivity of the films can be improved by either annealing in nitrogen gas or hydrogen plasma post-treatment, as a result of changes in the chemical and physical structure of the films. Finally a mechanism for the decomposition of TMT is proposed.