A semiconductor optical integrated device according to the present invention includes a conductive substrate, a laser provided to the conductive substrate, a semi-insulating semiconductor layer provided on the conductive substrate, a photodiode provided on the semi-insulating semiconductor layer and a waveguide that is provided on the conductive substrate and guides output light of the laser to the photodiode, wherein an anode of the photodiode and a cathode of the photodiode are drawn from an upper surface side of the photodiode, and the waveguide and the photodiode are separated from each other by the semi-insulating semiconductor layer.