Ag-doped SnS films have been grown with a thickness of similar to 0.5 mu m by thermal evaporation technique on Coring 7059 glass substrates at a substrate temperature of 275 S C. The effects of doping on the physical properties of the films have been investigated. The physical characteristics of the films are discussed and correlated to the microstructural and electro-optical properties. Electro-optical studies show that undoped SnS films have an electrical resistivity and optical bandgap of 35.6 Omega cm and 1.35 eV at room temperature. With the increase of Ag dopant concentration, the resistivity of the SnS layers initially decreased, reached a minimum value of 6.98 Omega cm at 15 atom % of Ag and again increased thereafter. However, optical bandgap (E-g) of the films decreased nonlinearly with increase of Ag percentage. An empirical formula E-g = 1.345-0.0014 X + 5.952 x 10(-5) X-2, which describes the energy gap as a function of the film composition, has been derived. The doping effect on the surface structure of SnS films was also studied. (c) 2006 The Electrochemical Society.