Junctionless transistors are variable resistors controlled by a gate electrode. The silicon channel is a heavily doped nanowire that can be fully depleted to turn the device off. The electrical characteristics are identical to those of normal MOS-FETs, but the physics is quite different. Conduction mechanisms in Junctionless Nanowire Transistors (gated resistors) are compared to inversion-mode and accumulation-mode MOS devices. The junctionless device uses bulk conduction instead of surface channel conduction. The current drive is controlled by doping concentration and not by gate capacitance. The variation of threshold voltage with physical parameters and intrinsic device performance is analyzed. A scheme is proposed for the fabrication of the devices on bulk silicon. (C) 2011 Elsevier Ltd. All rights reserved.