To obtain an optical modulator which has the α parameter suitable for long-distance transmission and is low in the insertion loss at the time of a transmissible state by constituting the optical modulator with a quantum box for confining three-dimensional quanta.

Diffraction gratings 3 are formed on part of the surface of an n-type InP substrate 1 and an n-type layer 2 is formed on this substrate 1. A distribution feedback type (DFB) laser 14 and the optical modulator 15 are formed thereon by interposing a separating region 16 therebetween. The DFB laser 14 is formed by laminating an n-type clad layer 2, an active layer 4a, a p-type clad layer 5, a p-type layer 6 and a contact layer 7a on the diffraction gratings 3. The optical modulator 15 is formed by laminating a modulation absorptive layer 4b including a quantum box on the n-type layer 2 and laminating p-type layers 5, 6 and p-type contact layer 7b thereon. A polyimide region 9 is formed on the periphery of the p-side electrode 10b and a wiring layer 11 formed thereon is connected to the p-side electrode 10b. Further, an n-side electrode 12 is commonly formed on the rear surface of the substrate 1.