The influence of an external magnetic field on optical features of semiconductor exciton spectra is researched in this work. It is shown that the magnetic field brings about the shift of the exciton level in the high-energy spectrum area. This causes the arising of a unique effect-- brightening-- of the crystal on the fixed external excitement frequency with the growth of the magnetic intensity value. The combination of electronic and magnetic characteristics of a crystal in an exciton frequency region opens new possibilities of giving control over the bistable behavior of the crystal. It is shown that the magnetic- optical response of a semiconductor on laser excitation generates bistable loops, both on the intensities of falling light (tau) (T) and in the size of the magnetic field-- (tau) (Hyields).