The theory of self‐diffraction of light by transient free‐carrier gratings in semiconductors has been expanded to the case in which nonlinear absorption of light creates the grating. Its application to the experiments performed allowed determination of the free‐carrier ambipolar diffusion coefficients in CdS, CdSe, and ZnSe crystals, and the mechanism of free‐carrier recombination and carrier lifetime in CdS at low temperatures.