An image sensor includes a substrate, a first isolation region defining a unit pixel, a first photoelectric conversion region in the unit pixel, a second photoelectric conversion region in the unit pixel, the second photoelectric conversion region spaced apart from the first photoelectric conversion region, a floating diffusion region, the floating diffusion region adjacent to the first surface of the substrate, a first transfer gate on the first surface of the substrate, the first transfer gate between the first photoelectric conversion region and the floating diffusion region, and a second transfer gate on the first surface of the substrate, the second transfer gate between the second photoelectric conversion region and the floating diffusion region. At least a part of the first transfer gate is buried in the substrate, and a bottom surface of the first transfer gate is different in height from a bottom surface of the second transfer gate.