Insituoptical reflectometry at the wavelength of 488 nm was employed to control the growth of MgZnSSe/ZnSSe Bragg mirror stacks for the blue‐green spectral region. 10‐ and 20‐period layer structures of MgZnSSe/ZnSSe were grown on GaAs (100) epilayers by molecular beam epitaxy. A room‐temperature peak reflectance of 86% was obtained for the 20‐period structure at the central wavelength of 474 nm. The results show that, in general,insituoptical monitoring of growth is a viable and simple method for real‐time layer thickness control of MgZnSSe/ZnSSe quarter‐wave stacks. ©1995 American Institute of Physics.