Accurate control of distance between suspended semiconductor nanowires and substrate surface

A semiconductor device comprising:

• a first buried oxide layer portion and a second buried oxide layer portion each located on an uppermost surface of a buried boron nitride layer, wherein a portion of said uppermost surface of said buried boron nitride layer between said first and second buried oxide layer portions is exposed;
• a first semiconductor pad located atop said first buried oxide layer portion;
• a second semiconductor pad located atop said second buried oxide layer portion;
• a plurality of semiconductor nanowires connecting the first semiconductor pad and the second semiconductor pad in a ladder-configuration and suspended above said exposed portion of said uppermost surface of said buried boron nitride layer;
• a gate dielectric surrounding each semiconductor nanowire and located directly on a top surface and a bottom surface of each semiconductor nanowire;
• a gate surrounding each semiconductor nanowire and located directly on a surface of each gate dielectric;
• and
• a gate dielectric portion located directly on a surface of said exposed portion of said buried boron nitride layer, and in contact with a surface of said gate located beneath each semiconductor nanowire.