Horizontal and vertical tunneling field-effect transistors (TFETs) having an abrupt junction between source and drain regions increases probability of direct tunneling of carriers (e.g., electrons and holes). The increased probability allows a higher achievable on current in TFETs having the abrupt junction. The abrupt junction may be formed by placement of a dielectric layer or a dielectric layer and a semiconductor layer in a current path between the source and drain regions. The dielectric layer may be a low permittivity oxide such as silicon oxide, lanthanum oxide, zirconium oxide, or aluminum oxide.