PURPOSE: To realize a strained quantum well type laser diode of higher reliability, by making the lattice constant of a quantum well active layer differ from that of a barrier layer by a specified amount, and setting the lattice orientation of the quantum well active layer to the neighborhood of (111).

CONSTITUTION: On an N-GaAs substrate 1 having the face orientation shifted by 0.5° from the (111) B face toward the (100) face, each of the layers 2-10 is continuously formed by using a molecular beam epitaxy method. In this process, A GaAs and Inlays are formed under the optimum conditions, at a high growth temperature and a low growth temperature, respectively. The lattice constant of a quantum well active layer 6 is made different of the lattice constant of a barrier layer 5 adjacent to the quantum well active layer 6 by 0.1% or more, and the lattice orientation of the active layer 6 is set to the vicinity of (111). In the above strained quantum well type laser diode, stress is applied parallel to the quantum well layer, but deterioration of the interface can be restrained by setting the lattice orientation of the active layer to be in the neighborhood of (111).