Heterojunctions have been fabricated by deposition of amorphous gallium arsenide on p-type crystalline silicon. C(V) and J(V) measurements were performed to determine electrical properties of these structures. Rectifying properties have been obtained, and capacitance-voltage behavior indicates an abrupt interface with a main discontinuity in the valence bands. The forward current involves tunneling and is successfully explained by a multi-tunneling capture-emission model. The reverse current is probably limited by the generation process.