CdS films were prepared by chemical bath deposition (CBD) at 60degreesC without stirring. The crystallographic structure of the films and the size of the crystallites in the films were studied by X-ray diffraction. The energy gap of the films was found to decrease by annealing. The best annealing temperature for CBD grown US films was found to be 300degreesC from the optical properties. Optical properties of the films were calculated using the envelope method. The refractive index was found decreasing with wavelength and annealing. The crystallite sizes were found to increase, and the X-ray diffraction patterns were seen to sharpen by annealing. The optical properties of the films were seen to be dependent on the film thicknesses. The band edge sharpness of the optical absorption was seen to oscillate by thermal annealing. Self-oxidation and sulfur evaporation were found responsible for this oscillating behavior. Annealing over 300degreesC was seen to degrade the optical properties of the film. (C) 2003 Elsevier B.V. All rights reserved.