A MOSFET structure includes a planar semiconductor substrate, a gate dielectric and a gate. An ultra-thin (UT) semiconductor-on-insulator channel extends to a first depth below the top surface of the substrate and is self-aligned to and is laterally coextensive with the gate. Source-drain regions, extend to a second depth greater than the first depth below the top surface, and are self-aligned to the UT channel region. A first BOX region extends across the entire structure, and vertically from the second depth to a third depth below the top surface. An upper portion of a second BOX region under the UT channel region is self-aligned to and is laterally coextensive with the gate, and extends vertically from the first depth to a third depth below the top surface, and where the third depth is greater than the second depth.