Abstract: In a TRS (twin ridge substrate) type semiconductor laser, reflectivity at both facets of the resonator at the oscillation wavelength is selected to be higher than the reflectivity of the semiconductor crystal of the laser device, but smaller than 1, thereby stabilizing the light oscillation with a low S/N ratio.

Abstract: A semiconductor substrate having a groove with a dove-tail-shaped cross section is used as a substrate and thereon, several epitaxial layers including an active layer are formed and a current injection region is formed immediately above the groove; the semiconductor laser attains a high power lasing with the fundamental transverse mode.

Abstract: The invention provides a chemical etching method for a semiconductor device, which comprises a step of forming a first layer of Ga.sub.1-x Al.sub.x As (0.ltoreq.x<1) having a surface (100), a step of forming on the first layer a second layer of Ga.sub.1-y Al.sub.y As (0.ltoreq.y<1) having a surface (100), and a step of chemically etching the layers from a level above the second layer and along the direction of <011>. The slope angle of etch face of the second layer depends on the mol fraction y of the second layer, and the slope angle of etch face of the first layer depends on the mol fraction y of the second layer and the mol fraction x of the first layer. These facts are best utilized in the invention so that the etch profile of the first layer may have a desired slope angle.