An experimental study has been made of the anodic dissolution of n‐type under illumination. In the dark, the dissolution potential depended on the carrier concentration and the surface orientation of the sample. By illuminating the surface of the sample, the dissolution potential became less noble and its dependence on carrier concentration and surface orientation became small with increasing light intensity. Samples were electropolished under the condition that the surface orientation dependence of the dissolution potential was scarcely observed. In electroetching under illumination, flat‐bottomed holes were obtained and the etched depth was controlled with an accuracy better than 0.1 μm. Under illumination, a damaged surface exhibited less dissolution than that of an undamaged surface. With the introduction of surface damage to selected regions of the substrates by nitrogen‐ion bombardment, selective etching without the use of protective masks has been carried out.