The effects of quantum confinement on transport properties of silicon nanowire metal-oxide-semiconductor field-effect transistors (FETs) and single-electron transistors are experimentally investigated. By carefully designing the channel width, the nanowire transistors operate as silicon nanowire FETs (SNWFETs) or single-charge transistors. Large quantum confinement in ultranarrow silicon nanowires plays a key role in these devices. We also adopt a special device configuration in which both n-type and p-type operations can be attained in an identical device, and the dependence on the channel direction and charge polarity is intensively investigated. Statistical measurements and band structure calculation reveal that  p-channel SNWFETs show smaller threshold voltage variations and  single-hole transistors show the largest Coulomb blockade oscillations at room temperature.