Fully depleted silicon-on-insulator metal-oxide-semiconductor field effect transistors with junction-isolated back gate electrodes formed by implanting bet-on through the silicon film and buried oxide into lightly doped n-type separation by implantation of oxygen substrates have been studied experimentally and through numerical device simulation. The useful range of threshold adjustment by back gate biasing is shown to be approximately +/-300 mV for typical structures, irrespective of silicon film or buried oxide thickness, and is limited primarily by accumulation or inversion of the back surface of the silicon him for extreme values of back fate bias.