PROBLEM TO BE SOLVED: To provide a method for producing an optical semiconductor device, by which timing for stopping etching of a resin or a resist on a projection part such as a ridge shape or a mesa shape can be easily and accurately determined.SOLUTION: The method for producing an optical semiconductor device comprises producing an optical modulator that guides light in an optical waveguide interposed between a pair of grooves, and the method includes the steps of: forming a plurality of pairs of evaluation grooves 31a, 31b in an evaluation region (TEG (test element group) region) set on a wafer 16; applying a resin layer 13 on the wafer 16; etching the resin layer 13 to expose a top of the optical waveguide; and forming an electrode on the optical waveguide. The width of the plurality of pairs of evaluation grooves 31a, 31b in the evaluation region differs by each pair, and in the exposure step, a top of a region 33 interposed by at least one pair of evaluation grooves 31a, 31b in the evaluation region is exposed by etching.