We report the effects of the spacer and the single-charge trap (SCT) on the voltage transfer characteristics of cylindrical-shape gate-all-around (GAA) silicon (Si) nanowire (NW) metal-oxide-semiconductor field effect transistor (MOSFETs). We explore the impact of low-x spacer, high-x spacer, and dual spacer (DS) on electrical characteristics of the GAA Si NW MOSFET with a gate length of 10 nm. Compared with the nominal device (i.e., the device without spacer), the device with DS possesses 68.8% reduction on the normalized off-current and 29.4% increase on the normalized on-current for n- and p-type devices. Similarly, 21.1% and 3.38% improvements on the normalized high and low noise margins can be achieved for the GAA Si NW complementary metal-oxide-semiconductor (CMOS) circuit. Notably, the voltage transfer characteristics induced by the acceptor- and donor-type SCT for the CMOS circuit with DS possesses 2.64% and 3.82% enhancements for the normalized high and low noise margins compared with the nominal one.