(Bi0.6Sb0.4)2Te3 thin films of different thicknesses were deposited by the flash evaporation method onto cleaned glass plates held at room temperature. Structural characterization was carried out using x-ray diffraction and transmission electron microscopy which revealed that the films are polycrystalline and the grain size increases with increasing thickness. Electrical resistivity was measured in the temperature range 300-450 K during two cycles of heating and cooling. During the first heating, irreversible behaviour of conductivity has been observed. Semiconductor-like behaviour has been observed in the annealed films and also during the first cooling and subsequent heating-cooling cycles. The activation energy for conduction (in annealed films) is found to be thickness dependent and this can be explained with the help of the grain-boundary trapping model. The thickness dependence of electrical resistivity (in annealed films) has been analysed using the effective mean free path model. From the analysis, important material constants like the mean free path and the electron concentration have been evaluated.