A method for producing a semiconductor optical device, includes the steps of: (a) forming a semiconductor region on a substrate, the substrate including first and second areas; the first area including device sections (b) forming a first mask on the semiconductor region, the first mask including first patterns periodically arranged in the first area and a second pattern provided in the second area; (c) forming a plurality of periodic structures in each of the device sections and a monitoring structure in the second area by using the first mask, the periodic structures respectively corresponding to the first patterns, the monitoring structure corresponding to the second pattern; (d) measuring a shape of the monitoring structure; (e) selecting a desired periodic structure from the plurality of periodic structures on a basis of a result of measuring the shape of the monitoring structure; (f) forming a second mask including a pattern on the desired periodic structure; and (g) forming stripe mesas including the desired periodic structure by using the second mask.