A semiconductor device is disclosed. The semiconductor device provides a substrate comprising an image sensor region and a circuit region, wherein the circuit region comprises a pad region and a connecting region. A multilayer interconnect structure is formed on the substrate, wherein the multilayer interconnect structure comprises a plurality of dielectric layers, a plurality of lower wirings at the pad region and the connecting region, and a top wiring on at least one of the lower wirings at the connecting region. A passivation layer is formed over the multilayer interconnect structure. A pad structure is formed through the passivation layer and at least one of the dielectric layers on and electrically connected to at least one of the lower wirings at the pad region.