Flow patterns have been made visible in a horizontal water‐cooled epitaxial reactor by injection of particles into the gas flow. From these experiments, a stagnant layer model has been developed with which the epitaxial growth of silicon from silane can be described. In the case of a nontilted susceptor, the model predicts an appreciable nonuniformity in thickness along the susceptor, whereas a small angle of tilting of the susceptor should yield a much better uniformity in thickness (2% over a length of 22 cm). Experiments agree very well with the theoretical predictions of the model.