A method for producing a semiconductor optical device includes a first etching step of etching a stacked semiconductor layer with a first mask to form a stripe-shaped optical waveguide, the stripe-shaped optical waveguide including first and second stripe-shaped optical waveguides formed on first and second regions of a substrate, respectively; a step of forming a second mask on the stacked semiconductor layer with the first mask left; and a second etching step of etching the stacked semiconductor layer on the first region with the first and second masks. The second mask has a pattern for forming a mesa structure and includes an opening including first and second opening edges remote from side surfaces of the first stripe-shaped optical waveguide. The mesa structure is formed of the first stripe-shaped optical waveguide in the second etching step. The second stripe-shaped optical waveguide formed in the first etching step has a ridge structure.