This paper reports the function of the parasitic bipolar device in the 40 nm PD SOI NMOS device with the floating body effect. Using a unique extraction method, the function of the parasitic bipolar device during DC and transient operations could be modelled. During the turn-on transient by imposing a step voltage from 0 V to 2 V on the gate, the case with the a slower rise time shows a relatively faster turn-on in the drain current due to a stronger function of the parasitic bipolar device from smaller displacement currents through the gate oxide, as reflected in the current gain, as verified by the experimentally measured result. (C) 2011 Elsevier Ltd. All rights reserved.