This invention relates to an apparatus for gas source molecular beam epitaxy having a vacuum chamber (1) divided in to two spaces: a substrate heating space (P); and a crystal growth space (Q), so that the degree of vacuum in the substrate heating space (P) may be set lower that the pressure for Si growth and the degree of vacuum in the crystal growth space (Q) may be set corresponding to the pressure for Si growth to thereby grow Si based semiconductor with excellent reproducibility over a long period. <IMAGE>
