A semiconductor laser in which a PD unit monitoring an optical output is integrated is provided. A semiconductor laser (100) includes: a DFB unit including a back surface side first cladding layer (3), a first diffraction grating layer (9), a light emitting layer (1) having a first MQW structure and emitting a laser beam, a front surface side first cladding layer (6), and a first contact layer (12) which are stacked; a DBR unit including a back surface side second cladding layer (4) having a resistivity higher than that of the back surface side first cladding layer (3), a second diffraction grating layer (10) reflecting part of the laser beam toward the DFB unit, a first core layer (2a) guiding a remnant of the laser beam and having an effective bandgap energy smaller than that of the first MQW structure, and a front surface side second cladding layer (7) having a resistivity higher than that of the front surface side first cladding layer (6) which are stacked; and a PD unit including a back surface side third cladding layer (5), a second core layer (2b) having a second MQW structure absorbing the remnant of the laser beam guided by the first core layer (2a), a front surface side third cladding layer (8), and a second contact layer (14) which are stacked.