PURPOSE: To make the vertical etching step feasible for simplifying the manufacturing prosses by a method wherein, in order to dry etch the compound semiconductor region on a semiconductor substrate, the thickness of a photoresist is made larger than the etching depth of the semiconductor region.

CONSTITUTION: A GaAs substrate 101 is coated with a photoresist 102. At this time, the thickness of the resist 102 is made larger than the etching depth or the substrate 102. Next, a square pattern is formed by photolithographic step and then the substrate 101 is dryetched away by reaction ion beam etching step using chlorine gas. At this time, since the thickness of the resist 102 is made larger than the etching depth of the substrate 101, the processing section perpendicular to the substrate 101 can be formed. Through these procedures, only one layer of the resist 102 will suffice for a mask so as to simplify the manufacturing processes of a semiconductor device thereby making the vertical etching step feasible.