To switch a slope cutting means from a V blade to etching so as to provide a semiconductor device at a lower manufacturing cost, by a method wherein a semiconductor substrate having a crystal structure of zinc blende is subjected to a slope anisotropic etching in the direction of a forward mesa by the use of an etching aqueous solution which contains specific wt.% hydrogen chloride and hydrogen bromide, respectively.

A silicon nitride film 11 is formed on the surface of an InP substrate 10 as a semiconductor substrate that has a crystal structure of zinc blende, and a resist film 12 is applied on the silicon nitride film 11 and formed into a prescribed pattern 13. Openings are bored in the silicon nitride film 11 by etching using the pattern 13 as a mask. The substrate 10 is subjected to wet etching together with the silicon nitride film 11. As a result, a groove 14 with a slope of an angle of 45° in the direction of a forward mesa can be cut in the surface of the InP substrate 10. An etching solution contains hydrogen chloride and hydrogen bromide as main components, where 5 to 15 wt.% hydrogen chloride and 5 to 20 wt.% hydrogen bromide are contained in the etching solution. By this setup, a 45 slope forming process can be carried out through etching instead of a physical means.