Abstract: An image sensor includes photoelectric conversion device regions in a substrate; and an isolation structure extending in a direction from a first surface of the substrate to a second surface opposing the first surface, surrounding the photoelectric conversion device regions in a plan view, and having first regions adjacent to side surfaces of the photoelectric conversion device regions and second regions adjacent to each corner of the photoelectric conversion device regions. The isolation structure includes first isolation layers surrounding the photoelectric conversion device regions, respectively, second isolation layers surrounding the first isolation layers, first gap-fill patterns filling at least a portion of a space between the second isolation layers in the first regions, and second gap-fill patterns filling at least a portion of a space between the second isolation layers in the second regions, in the plan view.