This work presents a study on the influence of the design parameters on the ambipolar current (I-AMB) of the Tunnel Field Effect Transistors (TFETs). Using numerical device simulations. I-AMB is reduced progressively by underlapping the gate and the drain, by using low-k spacers and by placing the contacts in the top and bottom configuration. It is explained that a structure with top and bottom contacts leads to the field distribution inside the drain spacer, limiting the ambipolar current through the device. A TFET structure with ultra-low ambipolar current, totally independent of the gate voltage, is obtained by combining the layout of top and bottom contacts with low-k spacers. The scaling of the Silicon (Si) TFET is limited by the length of the drain spacer that cannot be scaled beyond a minimal limit without increasing I-AMB to undesired high values. (C) 2012 Elsevier Ltd. All rights reserved.