An image sensor includes a substrate region having a photoelectric conversion region and a floating diffusion region therein. The floating diffusion region is configured to receive charges generated in the photoelectric conversion region in response to light incident the photoelectric conversion region. First and second horizontal conductive lines are provided that extend on the substrate region, but at different heights relative to a surface of the substrate region. The first horizontal conductive line is electrically connected to the floating diffusion region and has a thickness smaller than a thickness of the second horizontal conductive line. In addition, the first horizontal conductive line extends closer to the substrate region than the second horizontal conductive line.