A semiconductor optical device including an SSC region includes a semiconductor substrate, a lower clad layer grown on the semiconductor substrate, and an upper clad layer grown on the lower clad layer. The semiconductor optical device with an SSC (Spot Size Conversion) area includes a gain area including an active layer grown between the lower clad layer and the upper clad layer to generate/amplify an optical signal; and an SSC (Spot Size Conversion) area including a waveguide layer extended from the active layer positioned between the lower and upper clad layers, such that it performs a spot size conversion (SSC) process of the optical signal generated from the gain area and generates the SSC-processed optical signal. The waveguide layer of the SSC area is configured to gradually reduce its thickness in proportion to a distance from the active layer, and the upper clad layer is etched in the form of a taper structure such that the taper structure has a narrower width in proportion to a distance from one end of the semiconductor optical device having the gain area to the other end of the semiconductor optical device having the SSC area.