Cadmium sulphide (CdS) plays an important role in the development of thin-film photovoltaic devices [1–5]. Hetrojunctions of CdS and other semiconductors such as CdTe, Cu2S, CuInSe2 and InP etc. have excited interest and made it possible to have efficient thin film solar cells. Low resistive CdS films are used in hetrojunctions in solar cells to lower the cell series resistance, whereas high resistive films are used for surface acoustic wave devices. The optimization of device characteristics requires a better understanding of the transport properties of these films. Electrical conductivity measurements are widely used in the characterization of transport properties of thin films [6–8]. It has been established that the boundaries between grains in the polycrystalline films play an important role in determining the conductivity of the films [9–11]. Many workers have grown CdS thin films using different deposition techniques such as thermal evaporation, spraying, chemical vapor deposition, sputtering etc. In this paper we report the electrical conductivity measurements of CdS thin films prepared by thermal evaporation. High purity (99.999%) cadmium and sulfur obtained from Johnson and Matthey (U.K.) were used in this investigation. An intimate mixture (8.01255 gm) of fresh powders of cadmium (150 μm) and sulfur (100 μm) in stoichiometric proportion corresponding to the composition CdS was placed in the graphite crucible. The crucible was kept in a transparent silica tube which after evacuation and insertion of argon (with oxygen impurity less than 2 ppm) was heated at a constant and reproducible rate of 3 K/min by a Thermal Program Controller (Make: ULVAC, Sinku Riku, Japan; Model: HPC-7000). The temperature of the sample was maintained constant at 900 K for 2 h and then heated again up to 1250 K at a rate of 5 K/min. It was held at 1250 K for 24 h and then furnace cooled to room temperature. The CdS sinter was taken out and ground into powder in a mortar and pestle. The formation of the compound was confirmed by X-ray powder diffraction patterns. Rectangular films (5 cm × 1.5 cm) of CdS varying in thickness from 1000 A to 5000 A were grown by the thermal evaporation technique in a vacuum ∼2 × 10−5 torr using a vacuum coating system (Make: HINDHIVAC; Model: 12A4DM). A molybdenum boat was used as the evaporation source and the substrates were cleaned glass plates held at room temperature, which were placed directly above the source at a distance of approximately 18 cm. The glass substrates were cleaned with freshly prepared chromic acid, detergent solution and distilled water, in that order and finally subjected to glow discharge cleaning. The growth rate and the thickness of the films were controlled in situ by a quartz crystal thickness monitor (Make: HINDHIVAC; Model: DTM 101). The deposition rate was kept at 1–2 A/s in all cases. Films of different thickness were prepared through different individual evaporations. For the electrical conductivity measurements, indium (In) contact films were used as they were found to make ohmic contact with the CdS film. The work function of In has been reported to be 4.12 eV and that of Cds to be >4.8 eV, which satisfy the condition for making ohmic contact [12]. The thick (∼2000 A) contact films were pre-deposited on both ends of the experimental film. Electrical resistance was measured using a Keithley Programmable Electrometer (Model: 617) while the temperature of the films was monitored using a copper-constantan thermocouple with the help of a Keithley DMM (Model: 196). Films were heated in vacuum ∼2 × 10−2 torr inside a tubular furnace. The rate of heating was kept at 3 K/min while hold time at the desired temperature was 10 min. After attaining the desired highest temperature, the films were subjected to furnace cooling.