An image sensor includes an active region including a photoelectric conversion region and a floating diffusion region, which are separated from each other, defined by a device isolation region on a semiconductor substrate, and a transfer transistor including a first sub-gate provided on an upper surface of the semiconductor substrate and a second sub-gate extending within a recessed portion of the semiconductor substrate on the active region between the photoelectric conversion region and the floating diffusion region, wherein the photoelectric conversion region includes a plurality of photoelectric conversion elements, which vertically overlap each other within the semiconductor substrate and are spaced apart from the recessed portion.