PURPOSE: To fabricate a fine structure possessing a quantum well function in two directions with ease.

CONSTITUTION: There are provided a first process wherein there is formed a multiple quantum well structure composed of a material A (Al0.5Ga0.5As layer 3) and a material B (Al0.2Ga0.8As layer 4), a second process wherein a cross section of the foregoing multiple quantum well structure is taken out, and a third process wherein there is formed on the foregoing cross section a first quantum well structure composed of a material C (Al0.7Ga0.3As layers 6, 10) and a material D (GaAs layer 7). Further, in the third process, there are set a quantum barrier of the first layer of a single quantum well structure and the width of the quantum well such that a carrier wave function in the single quantum well is influenced by the materials A and B.