PURPOSE: To improve the quality of an oxide film and also, exceptionally reduce warps by providing fault-free layers on the bottom and the side face of an island region.

CONSTITUTION: A first silicon substrate 1 and a second silicon substrate 2 which is a supporting substrate are coupled integrally through an oxide film 3. The first silicon substrate 1 is separated into a plurality of single crystal islands 5 by interelement isolating regions 4 reaching the oxide film 3. And, an oxide film 6 is also made on the inner face of the interelement separating groove 4. Though an oxygen deposit 8 exists in the single crystal island region 5, fault- free layers 9 are provided, respectively, on the bottom adjacent to the oxide film 3 and the side face adjacent to the oxide film 6. The thickness of this fault-free layer 9 is on a level that the oxygen deposit does not reach the oxide film 6 even in the later heat treatment, for example, it becomes fens of μm when maintained for about 10 min. or over at a temperature of about 1150°C in nonoxidating atmosphere.