PURPOSE: To prevent a narrow channel effect due to the growth of bird's beak without exeucting many steps of processes and simultaneously keep flatness of the semiconductor device surfaces and prevent the failure of wirings by utilizing CVD oxide film and SOG for separation and formation of elements.

CONSTITUTION: A semiconductor substrate 1 is coated with a resist 2, a pattern for element isolation region is formed on the resist 2 and the surface of the semiconductor substrate l in the element isolation region forming area is then etched. Next, the resist 2 is removed, a CVD oxide film 3 is grown on the surface of semiconductor substrate 1, and the CVD oxide film 3 is coated with SOG 4. Next, after SOG 4 is etched back, a gate portion and a wiring, etc., of the semiconductor device are formed. For instance, after SOG 4 and SVD oxide film 3 are etched, a gate oxide film 8, a gate electrode 9 and source/drain 5 of a transistor are formed and after an interlayer insulating film 6 is grown, a contact hole is made and a metal wiring 7 is formed.