To provide a semiconductor laser element which oscillates stably when an injection current is increased in a semiconductor laser element of a gain waveguide type whose stripe width is large.

A semiconductor laser chip 19 is bonded to a heat sink 1 via solder material 2. The side end surface of the element is inclined by an angle in the vicinity of Brewster angle of a TM mode. In the chip 19, a current is constricted by a P side electrode 3, an N-cap layer 4 and a P+ cap layer 5, an active layer of a strain quantum well 9 is sandwiched by a P-clad layer 7 and an N-clad layer 11 via guide layers 8, 10, and a quantum well laser sandwiched by a P-cap layer 6 and an N-GaAs layer 13 is formed. The gain of a TM mode is large, the gain of a TE mode is small, and the reflectivity of a TM mode light on the side end surface is made almost zero. As a result, stimulated emission in the transversal direction is restrained and stable laser oscillation is obtained.