An image sensor includes a semiconductor substrate including a pixel region and a pad region, a plurality of photoelectric conversion regions in the pixel region, an interconnect structure on a front surface of the semiconductor substrate, a pad structure in the pad region and on a rear surface of the semiconductor substrate, a through via structure in the pad region and electrically connected to the interconnect structure through the semiconductor substrate, and an isolation structure at least partially extending through the pad region of the semiconductor substrate from the rear surface of the semiconductor substrate. The isolation structure surrounds the pad structure and the through via structure in a plane extending parallel to the rear surface of the semiconductor substrate.