Zinc sulphide (ZnS) thin films are promising materials for optoelectronic and photovoltaic devices due to their wide band gap and high transparency. Their properties, however, are significantly influenced by deposition and annealing conditions. This study aims to synthesize and characterize ZnS thin films deposited at varying substrate temperatures using the spray pyrolysis method, and to examine the influence of temperature on their structural and optical properties. ZnS thin films were deposited on pre-cleaned glass substrates at substrate temperatures of 300 °C and 350 °C using a precursor solution of zinc acetate and thiourea. The films were subsequently annealed at 400 °C. X-ray diffraction (XRD) was used to analyze the structural properties, while UV-Vis spectroscopy was employed to study the optical behavior. XRD analysis revealed that all films exhibited a polycrystalline cubic structure with a preferential (111) orientation. The grain size increased from 20.74 nm to 28.70 nm with rising temperature. Optical measurements showed high transmittance (60–75%) in the visible and near-infrared regions. Band gap energies were found to decrease from 3.35 eV to 2.8 eV as substrate temperature increased. These results demonstrate that substrate temperature significantly affects the microstructure and optical response of ZnS films. In conclusion, the high transparency and tunable band gap make these ZnS films suitable candidates for solar cell windows and optoelectronic components, offering a cost-effective approach via spray pyrolysis.