In this work we report the study of the thermal and optical properties of polycrystalline CdS thin films deposited by the gradient recrystallization and growth technique. CdS films were grown on pyrex glass substrates. These studies were carried out using an open photoacoustic cell made out of an electret microphone. From X-ray diffraction, atomic force microscope and photoluminescence measurements we observed polycrystalline US films with good morphology and crystalline quality. We obtained a thermal diffusivity coefficient of our samples with values ranging from 3.15 to 3.89 x 10(-2) cm(2)/s. For comparison, we measured a value of 1.0 x 10(-2) cm(2)/s for the thermal diffusivity coefficient of a CdS single crystal. We measured an energy gap value of 2.42 eV for our samples by using a photoacoustic spectroscopy system. (C) 2008 Elsevier B.V. All rights reserved.