Provided is a semiconductor optical integrated circuit which consumes less electric power than a conventional semiconductor optical integrated circuit. A semiconductor optical integrated circuit (1) includes a semiconductor layer (13) in which (i) an optical waveguide (LG) including heated section I1 through I3 and (ii) heater parts H1 and H2 are provided. The optical waveguide (LG) meanders such that the heated sections I1 through I3 are juxtaposed to one another. Each heater part Hi is arranged between a heated section Ii and a heated section Ii+1 which are adjacent to each other.