Abstract: In a manufacturing method of a semiconductor device in the field of large-scale integrated circuits utilizing a trench isolation technique; said method includes the steps of: forming first and second films having stepped portions on first and second underlying films adjacent to one another; forming a conductive film so that the first and second films having stepped portions are also covered; forming a first resist mask for forming gate electrodes on the conductive film and simultaneously forming a second resist mask on at least part of the conductive film corresponding to the stepped portions of the first and second films, the first and second resist masks being simultaneously formed; dry-etching the conductive film through the first and second resist masks to form gate electrodes while leaving the conductive film on the stepped portions of the first and second films; and removing the first and second resist masks.