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Thin films of SnS have been prepared by chemical bath deposition and thermally treated in argon atmosphere at different temperatures. As-prepared films were polycrystalline of an orthorhombic structure, but at the thermal treatment of 300 • C their preferential orientation increased. The optical bandgap and the type of transition are determined by the transmittance spectrum. The value of the optical bandgap is determined for the direct transitions of 1.38 eV which is not changed by the thermal treatment. The optical bandgap for the indirect transitions increased with the time of thermal treatment, and also the energy of phonon is estimated. From the red edge of the photoconductivity spectrum, a bandgap of E g(ph) = 1.24 eV was also determined. An impurity level with an activation energy of 0.39 eV and a thermal bandgap of E g(T ) = 1.19 eV are determined by the temperature dependence of the dark resistance of the films.