Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device, comprising:

• (1) the step of forming a first insulating film on at least one of one major surface of a first monocrystalline silicon substrate and one major surface of a second monocrystalline silicon substrate;
• (2) the step of directly joining said one major surface of said first monocrystalline silicon substrate and said one major surface of said second monocrystalline silicon substrate and annealing the resultant structure, thereby forming a bonded silicon substrate having said first insulating film on a contact surface;
• (3) the step of forming a first groove from the other major surface of said first monocrystalline silicon substrate of said bonded silicon substrate, extending through said first insulating film to reach said one major surface of said second monocrystalline silicon substrate;
• (4) the step of forming a second insulating film on the side walls of said first groove;
• (5) the step of forming a silicon layer on a surface of said bonded silicon substrate having said first groove using an epitaxial method, so that a monocrystalline silicon layer is formed above said first groove and a polysilicon layer is formed on said second insulating film formed on said side walls of said first groove;
• and
• (6) the step of polishing the resultant surface of said bonded silicon substrate to obtain a flat surface;
• thereby forming an island-like element formation region dielectrically isolated from another region by said first and second insulating films on said first monocrystalline silicon substrate.