An image sensor includes a substrate, a shallow trench isolation layer, a first deep trench isolation layer, and a second deep trench isolation layer. The substrate includes a first surface, a second surface opposing the first surface, and a plurality of unit pixel regions. The shallow trench isolation layer is adjacent to the first surface. The first deep trench isolation layer is adjacent to the shallow trench isolation layer and extends toward the second surface in the substrate. The second deep trench isolation layer is adjacent to the second surface and vertically overlaps the first deep trench isolation layer. The first and second deep trench isolation layers isolate the unit pixel regions from each other.