In this study, a double heterostructure of ZnSxSe1-x/ZnS0.86Se0.14/GaP has been grown by metalorganic vapor phase epitaxy. There is a transition region between the substrate and epilayer. The sulfur concentration on growing surface is a crucial point for the quality of the following layer. The bottom confinement layer ZnS0.86Se0.14 lattice-matched to GaP substrate shows energy gap 3.3 eV with photoluminescence full width at half maximum of 60 meV at 77 K. The active layer ZnS0.42Se0.58 with energy gap 2.98 eV shows photoluminescence full width at half maximum of only 28 meV at 77 K. There is 320 meV energy gap difference that is sufficiently high for carrier confinement in double heterostructure. However, the energy gap difference between the top confinement layer and the active layer is only 139 meV which can not be modulated furthermore by the flow rate ratio of hydrogen selenium and hydrogen sulfur. It is from the strain between two epilayers.