We have grown Bi doped SnS thin films using a novel procedure based on sulfurization of a thin film of the Sn:Bi alloy, deposited by evaporation. The effect of the Bi concentration on the optical and structural properties, as well as on the chemical composition of the SnS:Bi thin films was studied through spectral transmittance, X-ray diffraction (XRD) and Auger electron spectroscopy (AES) depth profile, respectively.