A method for manufacturing a semiconductor optical device includes: forming a p-type cladding layer; forming a capping layer on the p-type cladding layer, the capping layer being selectively etchable relative to the p-type cladding layer; forming a through film on the capping layer; forming a window structure by ion implantation; removing the through film after the ion implantation; and selectively removing the capping layer using a chemical solution.