Provided is an image sensor including a semiconductor substrate having a first surface and a second surface opposite each other, an organic photoelectric conversion device on the first surface of the semiconductor substrate, a through electrode structure connected to the organic photoelectric conversion device, and a pixel separation structure extending from the first surface toward the second surface of the semiconductor substrate. The semiconductor substrate may include a photoelectric conversion region in the semiconductor substrate. The pixel separation structure may surround the photoelectric conversion region when viewed in plan. The pixel separation structure may include a separation conductive pattern and a first sidewall dielectric pattern. The first sidewall dielectric pattern may continuously extend from between the separation conductive pattern and the semiconductor substrate to between the semiconductor substrate and a sidewall of the through electrode structure. A portion of the pixel separation structure penetrated by the through electrode structure.