The influence of the dimensionality on the performance of tunneling field-effect transistors is investigated with simulations. It is shown that in a three-dimensional tunneling FET it is possible to achieve inverse subthreshold slopes smaller than 60 mV/dec. However, there is a trade-off between high on-currents and small values for the subthreshold swing. Using a carbon nanotube tunneling FET as an example it is shown that in contrast to the 3D case, one-dimensional systems offer the possibility to combine a high on-state performance with steep inverse subthreshold slopes. (c) 2007 Elsevier Ltd. All rights reserved.