As-deposited bismuth sulfide thin films prepared by means of a chemical bath deposition were treated with argon AC plasma. In this paper, we present the results on the physical modifications which were observed when a pre-treatment, containing a solution of 1 M sodium hydroxide, was applied to the glass substrates before depositing the bismuth sulfide. The bismuth sulfide thin films were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy, UV-VIS, and electrical measurements. The XRD analysis demonstrated an enhancement in the crystalline properties, as well as an increment in the crystal size. The energy band gap value was calculated as 1.60 eV. Changes in photoconductivity (sigma(p)) values were also observed due to the pre-treatment in NaOH. A value of sigma(p) = 6.2 x 10(-6) (Omega cm)(-1) was found for samples grown on substrates without pre-treatment, and a value of sigma(p) = 0.28 (Omega cm)(-1) for samples grown on substrates with pre-treatment. Such sp values are optimal for the improvement of solar cells based on Bi2S3 thin films as absorber material. (C) 2015 Elsevier B.V. All rights reserved.