Structures for field-effect transistors and methods for fabricating a structure for field-effect transistors. A logic cell includes first and second field-effect transistors and a well defining a back gate that is arranged beneath the first and second field-effect transistors. A dielectric layer is arranged between the well and the logic cell. A plurality of deep trench isolation regions extend through the dielectric layer and are arranged to surround the first and second field-effect transistors and the well. The back gate is shared by the first and second field-effect transistors.