There is disclosed a monolithic semiconductor laser which is provided with an AlGaAs based semiconductor laser element (10a) and an InGaAlP based semiconductor laser element (10b) formed on a semiconductor substrate (1). The AlGaAs based semiconductor laser element (10a) is composed of an infrared light emitting layer forming portion (9a), which has an n-type cladding layer (2a), an active layer (3a) and a p-type cladding layer (4a) formed so as to have a ridge portion, and a current constriction layer (5a) provided on sides of the ridge portion, while the InGaP based semiconductor laser element (10b) is composed of a red light emitting layer forming portion (9a), which has an n-type cladding layer (2b), an active layer (3b) and a p-type cladding layer (4b) formed so as to have a ridge portion, and a current constriction layer (5b) provided on sides of the ridge portion. The current constriction layers of the both elements are made of the same material having a larger band gap than that of the active layer (3b) of the red light emitting layer forming portion. Consequently, there can be obtained a monolithic semiconductor laser capable of high temperature and high output operation without increasing the number of processes of the growth.