CdS/Si heterojunction has been fabricated by dc plasma sputtering technique. Polycrystalline CdS films have been prepared by dc plasma sputtering technique on Si substrate. The current – voltage under illumination showed that the photocurrent increases with increasing incident illumination intensity for CdS/Si heterojunction. The CdS thin films have been sputtered under vacuum of (9×10-2 ,8×10-2, 6×10-2,5×10-2) mbar, theheterojunction has better photovoltaic properties. The open circuit voltage (Voc) and the short circuit current (Isc)were found to vary with working discharge pressure, and the efficiency is 6.72% at 50.3 mW/cm2.