PURPOSE: To obtain a color filter having superior heat resistance and chemical resistance unlike a color filter of an org. material by forming an Al layer on a substrate for an image pickup element, anodically oxidizing the Al layer to form an alumina layer, and dyeing the alumina layer.

CONSTITUTION: An Al layer 2 of 2μm thickness is formed on a wafer 1 by vacuum deposition. A positive type resist 3 is spin-coated on the layer 2 to 5,000 thickness, exposed to ultraviolet rays, and developed to remove a part of the resist 3 on which a red filter is formed. The wafer 1 is immersed in dil. sulfuric acid, and the layer 2 is anodically oxidized to convert the part of the layer 2 not covered with the resist 3 into a γ-alumina layer 2'. The wafer 1 is further immersed in a red dye soln. to fill the soln. into the micropores in the layer 2', and the surface of the layer 2' is reacted with hydrogen in steam to cover the micropores. The resist 3 is then removed. Thus, a red filter R is formed.