PURPOSE: To avoid deterioration and improve reliability by a method wherein buried regions on both sides of an activation region contain at least one type of impurity among iron, chromium, vanadium, manganese and cobalt and the impurity is diffused into a part of the activation region to constrict the activation region.

CONSTITUTION: InP layers doped with iron (Fe) are buried as high-resistance current-blocking layers 14. An activation region 11 composed of an InGaAsP layer is surrounded by InP layers whose refractive index is smaller than the refractive index of the active region and whose forbidden band width is larger than the forbidden band width of the activation region. Fe is diffused about 0.2μm from the high resistance current blocking layers 14 to form diffusion fronts 20. These Fe-diffused regions 15 are also formed inside the active region 11 which has small forbidden band width. A as a result, the activation region 11 is constricted from both sides by about 0.2μm respectively to form a narrowed sidewise width. These Fe-diffused regions 15 form high resistance layers like the high resistance current blocking layers 14.