An ultra-low voltage performance of nanowire-transistors-based CMOS circuits is investigated using the Spice model parameters. All Spice model parameters of BSIM4 are extracted from measurement data of nanowire transistors fabricated on 300 mm SOI wafer. The delay time and the power consumption of NW-Tr.-based and bulk-Tr.-based CMOS circuits are examined. The operation voltage of NW-Tr.-based inverter is reduced 300 mV smaller than that of bulk-Tr.-based inverter due to the ideal sub-threshold slope. The performance benefits of NW-Tr.-based stacked circuit and SRAM cell are measured in terms of ultra-low voltage and ultra-low power operation.