Recently, a number of semiconductor devices have been widely researched in order to make breakthroughs from the short-channel effects (SCEs) and high standby power dissipation of the conventional metal-oxide-semiconductor field-effect transistors (MOSFETs). In this paper, a design optimization for the silicon nanowire tunneling field-effect transistor (SNW TFET) based on PNPN multi-junction structure and its radio frequency (RF) performances are presented by using technology computer-aided design (TCAD) simulations. The design optimization was carried out in terms of primary direct-current (DC) parameters such as on-current (I-on), off-current (I-off), current ratio (I-on/I-off), and subthreshold swing (SS). Based on the parameters from optimized DC characteristics, basic radio frequency (RF) performances such as cut-off frequency (f(T)) and maximum oscillation frequency (f(max)) were analyzed. The simulated device had a channel length of 60 nm and a SNW radius of 10 nm. The design variable was width of the n-doped layer. For an optimally designed PNPN SNW TFET, SS of 34 mV/dec and I-on of 35 mu A/mu m were obtained. For this device, f(T) and f(max) were 80 GHz and 800 GHz, respectively. (C) 2011 Elsevier B. V. All rights reserved.