An n-type first cladding layer, a first guide layer, a first enhancing layer, an active layer, a second enhancing layer, a second guide layer, and a p-type second cladding layer are sequentially stacked on an n-type GaAs substrate. The thickness of each of the first guide layer and the second guide layer is 100 nm or more. In such a semiconductor laser, the difference between the Eg (band gap energy) of the first guide layer and the Eg of the active layer (or the difference between the Eg of the second guide layer and the Eg of the active layer) is made 0.66 times or less of the difference between the Eg of the first cladding layer and the Eg of the active layer (or the difference between the Eg of the second cladding layer and the Eg of the active layer).