A fabrication technique for a vertical double-gate metal-oxide-semiconductor field-effect transistor (DG MOSFET) with a standing-up ultrathin channel (UTC) and self-aligned source and drain (S/D) is proposed. A 20 nm thick vertical UTC with low channel thickness fluctuation was formed on a (110)-oriented Si substrate using orientation-dependent wet etching. The top and bottom S/D were self-aligned to the DGs by using a combination of ion implantation and solid-phase diffusion. The fabricated vertical DG MOSFETs revealed that the channel thickness less influences the threshold voltage. Furthermore, a low sub-threshold slope of 68.8 mV/decade was achieved with a channel thickness of 20 nm.