A gate length of 25 nm and a silicon nanowire (SiNW) with a width of 6 nm and a height of 10 nm fully surrounded by a gate are demonstrated. A suspended SiNW, which is fully depleted, is fabricated on a bulk substrate by employing the deep reactive-ion etching process known as the Bosch process. The electrical characteristics and short-channel effects (SCEs) of the SiNW MOSFETs with all-around gates are presented. The fabricated devices show excellent immunity against SCEs despite their being built on a bulk substrate and having gate lengths scaled down to the 25-nm regime. Improved electrostatic characteristics that suppress the SCEs are shown when the dimension of the SiNW is reduced.