Single crystals of CdCr2Se4undergo a transition ("switching") from a low conductivity to a high conductivity state at a certain threshold electric field strength, as in Si-doped YIG. The appearing IV characteristics are similar to those of amorphous semiconductors. However, for the crystalline ferri-and ferromagnetic materials this switching is induced by well-defined transitions of electrons from narrowdand forpbands and/or doping levels into an initially unfilled broad conduction band by means of field ionization. In CdCr2Se4this is concluded from the characteristic temperature and magnetic field dependence of all critical electric values for the switching and instabilities which are causing negative resistance slopes. With an electrical field strength kept close to the critical value for switching, pure and doped magnetic semiconducting crystals could be switched to the high conductivity state by an applied magnetic field of less than 1 Vs/m2.