A 3D vertically stacked silicon nanowire (SiNW) field effect transistor featuring a high density array of fully depleted channels gated by a backgate and one or two symmetrical platinum side-gates through a liquid has been electrically characterized for their implementation into a robust biosensing system. The structures have also been characterized electrically under vacuum when completely surrounded by a thick oxide layer. When fully suspended, the SiNWs may be surrounded by a conformal high-K gate dielectric (HfO2) or silicon dioxide. The high density array of nanowires (up to 7 or 8 x 20 SiNWs in the vertical and horizontal direction, respectively) provides for high drive currents (1.3 mA/mu m, normalized to an average NW diameter of 30 nm at V-SG = 3 V, and V-d = 50 mV, for a standard structure with 7 x 10 NWs stacked) and high chances of biomolecule interaction and detection. The use of silicon on insulator substrates with a low doped device layer significantly reduces leakage currents for excellent I-on/I-off ratios >10(6) of particular importance for low power applications. When the nanowires are submerged in a liquid, they feature a gate all around architecture with improved electrostatics that provides steep subthreshold slopes (SS <75 mV/dec), low drain induced barrier lowering (DIBL < 20 mV/V) and high transconductances (g(m) > 10 mu S) while allowing for the entire surface area of the nanowire to be available for biomolecule sensing. The fabricated devices have small SiNW diameters (down to d(NW) similar to 15-30 nm) in order to be fully depleted and provide also high surface to volume ratios for high sensitivities. (C) 2014 Elsevier B.V. All rights reserved.