Undoped and doped CdS thin films have conveniently been prepared by conversion of cadmium oxide thin films using a chalcogen vapour. Dopants can be incorporated during the oxide formation stage, and the effects of three different dopants on the carrier transport properties are compared. Four X-ray diffraction peaks of the thin film polycrystalline material could be associated with the hexagonal (wurtzite) phase, two of the peaks are also consistent with the cubic (zincblende) phase. The reaction time required for the quantitative conversion of CdO to CdS decreased as the temperature increased, and quantitative conversion occurred in 30 min at 400ยฐC to give a Cd/S atomic ratio of 1.01. The absorption spectrum indicated a direct transition with a band gap of 2.42 eV. The surface of the sample appeared uniform and densely packe d with crystallites that are substantially smaller than 1 ixm. This preparation technique cap conveniently provide CdS films having a carrier concentration over the whole range of 1011 to 1017 cm -3. Likewise, the resistivities can be conveniently controlled with values ranging from 5 f~ cm to 5 x 107 1"~ cm. In addition, this material has been prepared by several other procedures described in the literature, and the properties of the films are compared.