A method for producing a spot size converter includes the steps of forming a first insulator mask on a stacked semiconductor layer; forming first and second terraces, and a waveguide mesa disposed between the first and second terraces by etching the stacked semiconductor layer using the first insulator mask, the first terrace having first to fourth terrace portions, the second terrace having fifth to eighth terrace portions, the waveguide mesa having first to fourth mesa portions; forming a second insulator mask including a first pattern on the first terrace portion, a second pattern on the fifth terrace portion, a third pattern on the third and fourth mesa portions, and a fourth pattern that integrally covers a region extending from the fourth terrace portion to the eighth terrace portion through the fourth mesa portion; and selectively growing a semiconductor layer by using the second insulator mask.