In this paper, we explored the characteristic fluctuations induced by various random discrete dopants (RDDs) on gate-all-around silicon nanowire metal-oxide semiconductor field-effect transistors. A 3-D quantum-mechanically corrected transport model was employed to analyze the simulated devices. The statistical results indicate that the variation of threshold voltage (Vth) not only can be reduced from 28.6% to 10.7% without channel doping and penetration from the source/drain into the channel, but also the variation of 3-dB frequency can be reduced from 8% to 2.7% due to the reduction of the variation of Vth. We reported that the high-frequency characteristic fluctuations (voltage gain and cutoff frequency) were dominated by electron mobility. This caused by RDDs from the drain extension exhibited less variability than that caused by RDDs from the source extension due to a reduced injection velocity near the S side and a negligible difference in the electron saturation velocity near the D side. This paper provides pertinent information on the design of high-frequency amplifier circuits in relation to devices with RDDs induced by variations in the semiconductor process.