An improved method for producing a semiconductor device in which overpolishing is prevented at a chemical mechanical polishing time to eliminate the influence of peripheries on the object part. A plasma oxide film is formed on a semiconductor substrate so as to fill a recess and a trench. With the use of a resist film as a mask, the plasma oxide film is selectively etched to leave an overpolish-preventing support member in a neighborhood of the recess, which is a photo-related mark, for providing a support against overpolishing at a chemical mechanical polishing time. The surface of the semiconductor substrate is polished by chemical mechanical polishing. Thereafter, a nitride film and an oxide film are removed.