An image sensor includes a substrate having a front side and a back side, an insulating structure containing circuits on the front side of the substrate, contact holes extending through the substrate to the circuits, respectively, and a plurality of pads disposed on the backside of the substrate, electrically connected to the circuits along conductive paths extending through the contact holes, and located directly over the circuits, respectively. The image sensor is fabricated by a process in which a conductive layer is formed on the back side of the substrate and patterned to form the pads directly over the circuits.