Semiconductor laser

In a semiconductor laser, including a semi-insulating substrate, first and second cladding portions, first and second electrodes, and an active region, the improvement wherein:

• said first and second cladding portions are formed on said semi-insulating substrate,
• said active region is formed between said first and second cladding portions,
• said first and second electrodes are respectively provided on said first and second cladding portions,
• said active region has a predetermined value of band gap,
• said first cladding portion includes a semiconductor layer having a larger value of band than said predetermined value and a pair of semi-insulating semiconductor layers respectively formed on top and bottom surfaces of said semiconductor layer and having values of band gaps greater than said larger value,
• said second cladding portion is of a reverse conductive type to that of said semiconductor layer and has a value of band gap greater than said predetermined value, and
• said laser further comprises a light guiding layer, wherein said active region is a portion of an active layer, said active layer and said light guiding layer face and contact each other and are formed between said first and second cladding portions and between said second cladding portion and said semi-insulating substrate, a first portion of said light guiding layer is in contact with said active region and a side wall of said semiconductor layer, and a second portion of said light guiding layer is in contact with said first cladding portion on periodical concave and convex surfaces.