The effect of a large static electric field on the Faraday and Voigt free‐carrier magneto‐optical effects in semiconductors is calculated for a parabolic band, for acoustic scattering, and for both high and low frequencies and low losses. It is shown that the electric field produces a larger relative change in the Voigt effect than in the Faraday, and that sizable effects may occur in all cases. Only the effect of the electric field on heating up the charge carrier distribution is considered, specifically directional effects being neglected. Comparison is made with experiments on indium antimonide.