Quantum-effects will play an important role in both future CMOS and ‘beyond CMOS’ technologies. By comparing single-electron transistors formed in un-patterned, uniform-width silicon nanowire (SiNW) devices with core widths from ∼5–40 nm, and gated lengths of 1 μm and ∼50 nm, we show conditions under which these effects become significant. Coulomb blockade drain–source current–voltage characteristics, and single-electron current oscillations with gate voltage have been observed at room temperature. Detailed electrical characteristics have been measured from 8–300 K. We show that while shortening the nanowire gate length to 50 nm reduces the likelihood of quantum dots to only a few, it increases their influence on the electrical characteristics. This highlights explicitly both the significance of quantum effects for understanding the electrical performance of nominally ‘classical’ SiNW devices and also their potential for new quantum effect ‘beyond CMOS’ devices.