A threshold voltage (V th) controllable multigate FinFET on a 10-nm-thick ultrathin BOX (UTB) SOI substrate have been investigated. It is revealed that the V th of the FinFET on the UTB SOI substrate is effectively modulated thanks to the improved coupling between the Si channel and the back gate. We have also carried out analysis of the V th controllability in terms of the size dependence such as the gate length (L G) and the fin width (T Fin).