A semiconductor device includes a semiconductor substrate, an insulating layer on a top surface of the substrate, and a first semiconductor transistor on the insulating layer, the transistor including an active region with a source region, a drain region, a channel region between the source and drain regions and a gate structure over the channel region, the gate structure extending beyond the transistor to an adjacent area. An outer well is included in the substrate, an inner well of an opposite type as the outer well situated within the outer well and under the active region and adjacent area, and a contact for the inner well in the adjacent area, the contact surrounding the gate structure. Operating the device includes applying a variable voltage at the contact for the inner well, a threshold voltage for the first transistor being altered by the variable voltage. The inner well and gate may be exposed and contacts created therefor together.