An image sensor includes a semiconductor substrate having a first surface and a second surface with a pixel region having photoelectric conversion regions, a gate electrode disposed on the pixel region and adjacent to the first surface, a first isolation structure extending from the first surface toward the second surface, the first isolation structure comprising a first pixel isolation pattern enclosing the pixel region, and a first inner isolation pattern spaced apart from the first pixel isolation pattern and positioned between the photoelectric conversion regions, and a second isolation structure extending from the second surface toward the first surface with a top surface vertically spaced apart from at least a portion of a bottom surface of the first isolation structure. The bottom surface of the first isolation structure is closer to the second surface of the semiconductor substrate than to the first surface thereof.