Thanks to ultimate Si nMOSFETs with physical gate length down to 16 nm, the main challenges related to conventional transistors have been estimated. Short channel effect control is difficult below 40 nm due to the large TED of BF2 halos. Nevertheless drain current higher than 800 muA/mum @ V-d = 1.5 V can be reached. Such performance is not a consequence of non-stationary effects since these are limited by the degradation of the low longitudinal field mobility on conventional short transistor. Ultimate transport is also analysed thanks to short and narrow devices. At low temperature, these MOSFETs are shown to operate like single electron transistors. (C) 2003 Published by Elsevier Ltd.