A new method of making good quality epitaxial layers for microwave applications is described. This technique uses trimethylgallium pyrolysis in the presence of arsine under reduced hydrogen pressure (20–100 Torr). At low pressure the autodoping phenomenon of the layer by the impurities of the substrate is eliminated, thus permitting the use of substrates heavily doped with tellurium. The memory effects taking place between the growth of layers of different carrier levels are reduced, the transient effects are reduced, all substrate‐layer, layer‐layer impurity profiles are more abrupt than at atmospheric pressure, and the effects of the chemical reactions taking place in the gaseous phase are reduced which means that large surfaces can be grown. Layers with residual impurity concentration lower than 1015 cm−3 have been obtained, n‐type layers intentionally doped with silicon by silane or with germanium by germane have been achieved. The decomposition kinetics of silane or germane always control the incorporation of these impurities.