We present the Fin-type double-gate metal-oxide-semiconductor field-effect transistors (FXMOSFETs, the XMOS transistor was named because its cross section resembles the Greek letter Ξ which corresponds to the English letter X) with ideal rectangular fin cross section, for the first time, using (110)-oriented silicon-on-insulator (SOI) wafers. The nanoscale silicon (Si)-Fin has successfully been fabricated by orientation-dependent etching using an etchant of 2.38% tetramethylammonium hydroxide (TMAH) solution. The almost ideal subthreshold slope of 64 mV/decade was obtained for the fabricated 20 nanometers (nm) Si-Fin and 145 nm gate length FXMOSFET. This excellent subthreshold characteristic experimentally shows that the interface property of the Si-Fin channel with (111)-oriented sidewalls is suitable to realize a high-performance FXMOSFET. The electrical characteristics of the fabricated FXMOSFETs in the 20–100 nm Si-Fin width regime have been systematically investigated. The experimental results indicate that the short-channel effects (SCEs) can be effectively suppressed by reducing the Si-Fin width to 20 nm or less. The developed processes are promising for fabrication of the FXMOSFET as a future nano-silicon device.