A silicon oxide layer is formed on a silicon substrate, and an opening whose wall is sloped inward is formed in the silicon oxide layer. A seed crystalline silicon layer is formed from the opening. The seed crystalline layer is selectively oxidized while leaving the seed crystalline layer required for crystal growth. An oxide formed at this time closes the opening. Consequently, the seed crystalline layer is insulated from the silicon substrate. The seed crystalline layer is epitaxially grown, to obtain a silicon growth layer on a field oxide layer. The growth layer is insulated from the silicon substrate, and is uniform in surface direction. Accordingly, there is no parasitic capacitance due to a p-n junction between the silicon substrate and the growth layer, thereby to make it possible to perform a high-speed operation. In addition, the growth layer is uniform in surface direction, thereby to make it easy to control the conditions set so as to obtain desired device characteristics in the manufacturing processes.