An image sensor includes a circuit substrate, a plurality of isolation regions, a plurality of photoelectric converters, and an insulation layer. The isolation regions are formed in a pixel region having the photoelectric converters formed therein with each photoelectric converter being electrically isolated by the isolation regions. The insulation layer is formed in a pad region with a substantially same depth as the isolation regions. The isolation region and the insulation layer are simultaneously formed for efficient fabrication of the image sensor.