Growth and characterization of CuInSe2 (CIS) thin films deposited on Si, for the purpose of forming heterojunctions to investigate the suitability of the material system for high efficiency solar cells, is reported here. Deposition was obtained by RF magnetron sputtering using a stoichiometric CIS target. As CIS and Si are closely lattice matched, large grain polycrystalline films were obtained. Rutherford backscattering spectroscopy (RBS) indicated that these CIS films have a composition of Cu 0.85In1.1Se1.9. Circular diodes were fabricated and the current- voltage characteristics of these diodes indicated that reasonable quality p-n junctions were obtained. The forward current of these devices increased by about three orders of magnitude, from 0.003 to 2.65 mA at a bias of 2 V when illuminated with a 75 watt halogen lamp. Large area samples 1 cm x 1 cm, were patterned with a window shaped contact and under illumination produced approximately 90 mV and 0.5 mA when measured in series with a precision multimeter and picoammeter. The strong response to illumination indicated that the material system has a high potential for use as a solar cell.