ZnS thin films have been successfully deposited with the same production parameters using thermionic vacuum arc technique on glass and silicon substrates. UV-Vis absorbance spectra and photoluminescence measurements were performed for the optical characterization of ZnS/glass thin film and ZnS/p-Si heterojunction device, respectively. The optical band gap is found approximately 3.78 eV. Further, electrical parameters of the device were determined for the current-voltage (I-V) measurements in dark and under illumination conditions. The open-circuit voltage and the short-circuit current values have been obtained related to illumination I-V measurements. Also, we have utilized photocurrent measurements to investigate the wavelength dependent to photosensitivity of the ZnS/p-Si heterojunction device.