When Ga or Al atoms are evaporated on a clean GaAs surface in an As‐free or a very low As pressure atmosphere, they are quite mobile and migrate very rapidly along the surface even at low temperatures. This characteristic is exploited for growing high‐quality GaAs and AlGaAs layers at very low temperatures by alternately supplying Ga and/or Al atoms and As4molecules to the GaAs substrate. Applying this method, AlGaAs‐GaAs single quantum well structures with excellent photoluminescence characteristics are grown at 300 °C.