An image sensor and a method of manufacturing thereof are provided. The image sensor includes a substrate, a grid structure, and color filters. The substrate includes a pixel separation structure defining pixel regions, and a sub-pixel regions for each pixel region. The grid structure is disposed on the substrate and includes first fence segments provided between the sub-pixel regions, and second fence segments provided between neighboring pixel regions. The grid structure defines openings corresponding respectively to the sub-pixel regions. The color filters are disposed in the openings defined by the grid structure. Each of the color filters has a flat top surface and the flat top surface of each color filter is parallel to a bottom surface thereof.