Sn-doped beta-Ga2O3 epitaxial layers have been grown on (100) beta-Ga2O3 substrates by metal organic vapour-phase epitaxy. Triethylgallium (TEGa), molecular oxygen (O-2) and tetraethyltin (TESn) were used as Ga, O and Sn precursors, respectively. Layers grown at optimized temperature and chamber pressure, i.e. 850 A degrees C and 5 mbar, had flat surfaces with a rms roughness of about 600 pm. Structural analysis by transmission electron microscopy revealed that the main defects in the layers were stacking faults and twin lamella. The incoherent boundaries of these defects are supposed to act as compensation and scattering centres, limiting the carrier mobility. Sn was homogeneously incorporated with a flat profile throughout the whole layer at concentration levels ranging from 2 x 10(17) to 3 x 10(19) cm(-3) proportionally to the used TESn flux. All layers were electrically conductive. However, an unambiguous Hall effect was measurable only for Sn concentrations higher than 1 x 10(18) cm(-3), resulting in electron concentrations from 5 x 10(17) to 2 x 10(18) cm(-3) at room temperature. For increasing free carrier concentrations, the electron mobility showed the tendency to increase from 10 to 30 cm(2)/Vs. The maximum mobility of 41 cm(2)/Vs, measured in a sample with free carrier concentration of 1 x 10(18) cm(-3), represents the highest value reported for beta-Ga2O3 layers grown by MOVPE so far.