The effective potentials for atomic motion on semiconductor surfaces are given in terms of the displacement–displacement correlation functions of the substrate by a Langevin equation approach. The method is illustrated by detailed calculations of the surface dynamics of the unreconstructed Si(100) surface for which several interesting new features are obtained. It is shown that the total effective potential for atomic diffusion on the surface differs substantially from the adatom‐rigid substrate interaction as a result of coupling to the dynamic substrate vibrations.