The possible factors which can determine the localized anisotropic photoetching ofn‐GaAs are analyzed. Mass transport to and from the reaction zone is considered. It is shown that diffusion of the oxidizing agent can become limiting when photoetching is performed by illumination of a masked pattern. Photogalvanic effects, leading to a delocalized dissolution mechanism, play a vital role under almost all practical conditions. Heating effects and local photostimulation of the dissolution reaction are of minor importance.