Disclosed is an improved method of growing an epitaxial layer preventing auto-doping from a doped region exposed to a surface of a semiconductor substrate. A surface of a semiconductor substrate of one conductivity type is covered with a mask having a predetermined opening. Then, impurity atoms are doped into the substrate through the opening to form a region of the other conductivity type. An epitaxial layer of one conductivity type is deposited over the exposed surface of the substrate with another mask which covers the entire surface of the region and has an area larger than that of the exposed surface of the region. The latter mask prevents auto-doping from the region of the other conductivity type. The process is usable for controlling, for example, channel widths of field effect semiconductor devices uniformly and precisely.