To provide a semiconductor laser capable of improving the noise characteristics of return light as well as maintaining self oscillation to high temperature.

On an n-GaAs substrate 101, there are formed an n-GaAs buffer layer 102, an n-GaInP buffer layer 103, an n-(Al0.7Ga0.3)0.5In0.5 P cladding layer 104, a un-(Al0.5Ga0.5)0.5In0.5P guide layer 105, an activity layer 106, a un-(Al0.5Ga0.5)0.5In0.5 P guide layer 107, a p-(Al0.7Ga0.3) 0.5 In 0.5 P first cladding layer 108, a p-(Al0.75Ga0.25)0.5In0.5P barrier layer 109, a p-(Al0.5Ga0.5)0.5In0.5P light guide layer 110, and a p-GaInP saturable absorption layer 111. The band gap of the barrier layer 109 is larger than the band gap of the first cladding layer 108.