A light emitting layer forming section (8) including an n-type conductivity type clad layer (2), an active layer (3) and p-type conductivity type clad layers (4) and (6) is laminated on a semiconductor substrate (1), and further, a contact layer (9) made of a material having substantially the same lattice constant and thermal expansion coefficient as those of the semiconductor substrate is laminated on the light emitting layer forming section. The light emitting layer forming section and the contact layer are formed in such a manner as to satisfy the following inequality: 1.5.ltoreq.(d.sub.1/d.sub.2).ltoreq.2.8, where d.sub.1 represents the thickness of the contact layer, and d.sub.2 represents the thickness of the light emitting layer forming section. As a consequence, it is possible to provide a semiconductor laser for a high output, in which a COD level can become high and a lifetime can be prolonged even if the light emitting layer forming section is as thick as 4 .mu.m or more.