To reduce the surface roughness and improve the MOSFET's electric characteristics, we introduce the Si(551) surface to replace the Si(110) surface, which is very easy to roughen during the wafer cleaning processes. We experimentally demonstrate the clearly improved characteristics of being much easier to flatten on the Si(551) surface using the repeated radical oxidation technology and the strong resistance to the alkali solution for suppressing the increase in surface roughness during the wafer cleaning processes. Basic electrical characteristics of the MOSFET are improved as much by fabricating on Si(551) compared to those fabricated on the Si(110) surface. We also theoretically and experimentally demonstrate that the MOSFET's performance has clearly been improved through the introduction of the accumulation-mode (AM) silicon-on-insulator (SOI) structure. Finally, a very high performance complementary metal oxide semiconductor (CMOS) has been successfully realized on the Si(551) surface by combining the radical oxidation silicon surface flattening technology and the AM device structure.