Nanoscale multigate field effect transistors (FETs) are potentially next-generation device candidates for achieving high performance targets of the ITRS due to their superior reduction of the short channel effects and excellent compatibility with planar CMOS fabrication process [1,2]. In this work, we for the first time numerically explore the high frequency characteristics of the sub-45nm silicon nanowire FET. Three-dimensional (3D) density-gradient-based device transport equations directly coupling with circuit equations are simultaneously performed for calculating the property of frequency response. Our result shows that the cut-off frequency of a well-designed sub-45nm nanowire FET with 100% surrounding gate is approach to 10 THz, which substantially benefits from the nature of infinite gate in the nanowire FET. Silicon-based nanowire FET devices as active components in microwave circuits draw people's attention for their extremely rich high frequency property [3, 4]. The extensive results and analyses are presented on the promising devices for high frequency analog applications.