A compound semiconductor thin film is formed by growing a plurality of molecular layers one over another. According to the present invention, while a carrier gas and a small quantity of hydride containing an element in Group V or VI are normally flowed, an organometallic compound which is diluted with hydrogen and which contains an element in Group III or II and a hydride which is diluted with hydrogen and which contains an element in Group V or VI are alternately introduced over a substrate so that an atomic layer of an element in Group III or II and an atomic layer of an element in Group V or VI are alternately grown over the substrate. According to this method, grown layers having a high degree of purity can be obtained. A portion such as a Ga-Ga two-layer structure formed in the growth of a surface of an element in Group III or II can easily be eliminated by the introduction of a hydrogen halide so that the surface defects and deep levels are significantly decreased and perfect crystals can be obtained. According to the present invention, a high-concentration doping of a III-V compound semiconductor becomes possible. The method of the present invention is advantageous in the fabrication of high-speed FETs and multi-quantum-well lasers using compound semiconductors.