A solid‐state diffusion theory is developed giving the distribution of impurities in epitaxial growth. It is shown that for most practical cases this theory takes on a particularly simple form. Extensive experiments were performed in the study of the distribution of the most common acceptor and donor type substrate impurities in silicon: boron and antimony. It is shown that the impurity distribution in most of the epitaxial film is uniform corresponding to the impurity doping of the SiCl4used in the epitaxial growth, and that the profile near the substrate—film interface is very close to the predictions of this simple theory. In addition, certain particular cases of interest were studied such as the spreading of a layer of impurities predeposited on the substrate surface prior to epitaxial growth, the effect of film growth rate on the impurity distribution, and the change in the impurity distribution during an additional high‐temperature step. In all cases, experiments and the solid‐state diffusion theory are in excellent agreement.