PURPOSE: To see that the implated ions do not spread sideways by implanting impurity ions from the direction where ion channeling occurs.

CONSTITUTION: An n-type epitaxial layer 2 is formed on a p-type board 1, and a mask 3 is made on the topside of this n-type epitaxial layer 2. Next, a specified place of the mask 3 is removed using a photolithography method, etching method, or the like so as to form a window to introduce impurities. Next, impurity ions such as boron ions, etc., are implanted from the direction where ion channeling occurs through this window. Hereby, the impurity ions are implanted deeply in longitudinal direction, and by a short time of thermal diffusion, an isolating region to separate the n-type epitaxial layer 2 is made. This way, the transverse width of the isolating region becomes narrow since the thermal diffusion is performed at low temperature for a short time, so micronization of the semiconductor element can be materialized.