[en] Large area 25 cm/sup 2/, cadmium sulfide (CdS) thin films were deposited by thermal evaporation technique in an oil pumped industrial vacuum system operating in the range of 10/sup -7/ to 10/sup -7/ Torr. The films were produced at different substrate temperatures in the range of 100 to 300 deg. C. It has been observed that the substrate temperature during deposition plays an important role in controlling the electrical and optical properties of the films. Transmittance versus wavelength measurements in the range of 300 to 2000 nm of the deposited films observed that the films had high transmittances > 80%) in infrared region and were highly absorbing with a sharp absorption edge at a wavelength of about 510 nm. The transmittance and Reflectance versus wavelength data corresponding to the above absorption edge revealed an optical bandgap of 2.42 eV. Using the Van der Pauw technique the electronic properties such as resistivities and mobilities of the deposited films were studied. Stoichiometric films were highly resistive but films produced at optimum deposition conditions had resistivities of 10 to 150 omega cm and mobilities in the range of 2 to 90 cm/sup 2/V/sup -1/s/sup -1/. The Scanning Electron Microscope (SEM) was used to study the morphology of the deposited films. SEM micrographs showed that there was a progressive increase in the grain size and columnar growths as the substrate temperature was increased from 150 to 300 deg. C. (author)