An integrated semiconductor laser-modulator device less affected by a fluctuating electric field due to modulating signals applied to the modulator has improved frequency characteristics. The integrated semiconductor laser-modulator includes an active layer, a beam waveguide layer having a bulk structure with a bandgap energy larger than that of the active layer but smaller than that of a laser beam absorption layer having a bulk structure, wherein waveguides of the laser and modulator are connected and aligned, and a cladding layer including a diffraction grating is disposed on top of or beneath the waveguides.