In this paper, a novel ZnO/graphene/porous silicon hybrid device is fabricated and its electrical behaviors are studied along with a ZnO/graphene/silicon device. Graphene (G) is prepared by exfoliation of graphite foil in aqueous solution of inorganic salt. Porous silicon (PS) is fabricated by electrochemical etching of p-type silicon (Si). Graphene is deposited on the surface of Si and PS substrates by thermal spray pyrolysis method. ZnO rods are grown on the samples by using catalyst-free chemical vapor transport and condensation method. The currentvoltage relationships of ZnO/G/Si and ZnO/G/PS devices are studied under different volumes of graphene solution. The results reveal the distinctive features of the I-V characteristics of the two devices for different volumes of graphene solution under room light as well as UV illumination.