AbstractAn ultra‐high vacuum silicon selective epitaxial method has been used in the LSI process for the first time. Using this epitaxial growth method, the gap between the oxide film pattern and epitaxial layer (facet width) is as small as 0.03 μm and selective epitaxial growth can be produced in the microscopic active regions. Therefore, this method is suitable for reducing device size. The leak currents between source and drain and between devices are comparable with those in Si‐bulk MOS devices, indicating that crystalline defect density is small in this epitaxial film. The channel in the MOS transistor formed using this epitaxial layer is extremely small. Transconductance of an nMOS transistor with an extremely short and narrow channel (gate length 0.1 μm and gate width 0.3 μm) was 530 mS/mm.