PURPOSE:To eliminate the mismatch of the lattice constants including the misfit caused by impurities, by changing the composition ratio of a mixed crystal in the case the forbidden bandwidths of II-VI group compound semiconductors are different. CONSTITUTION:The lattice constants and the forbidden bandwidths of known II-VI group compounds are availabel. In general, the lattice constants of trielemental mixed crystals II1-xII'xVI indicates linear relationship between II-VI and II'-VI in accordance with the Vegard's rule and the forbidden bandwidths can be mostly approximated by the linear relationship. All the II-VI compounds have a direct transition type band structure. Therefore, for example, if the lattice constant and the forbidden bandwidth are calculated by adjusting the mixed crystal ratio (x) of ZnSe and CdSe so as to make the result agree with CdS in preparing the hetero-junction of CdS and ZnSe1-xTex, the misfit can be eliminated, the carrier injecting efficiency can be improved, and the semiconductor laser with high efficiency and long life can be obtained.