The theory of non‐linear response of an electronic subsystem in planar multi‐layer structures (including quantum wells) to a strong electromagnetic field is developed. On the basis of the exact Hamiltonian of the electron‐phonon interaction for such structures a non‐linear dielectric permittivity tensor is obtained by the statistical operator method in the path integration representation. In the three‐layer structures with a thin middle semiconducting layer and moderate values of the dielectric permittivity of the outer dielectric media the contribution to the absorption due to the interaction of electrons with surface phonons is found to prevail over that of bulk phonons and to ensure a substantially more rapid rise in the absorption coefficient with increasing intensity in comparison with the case of a semiconductor crystal.