Tunneling Field Effect Transistors (TFETs) are promising devices in that they promise significant performance increase and energy consumption decrease due to a steeper subthreshold slope (for example, smaller sub-threshold swing). In various embodiments, vertical fin-based TFETs can be fabricated in trenches, for example, silicon trenches. In another embodiment, vertical TFETs can be used on different material systems acting as a substrate and/or trenches (for example, Si, Ge, III-V semiconductors, GaN, and the like). In one embodiment, the tunneling direction in the channel of the vertical TFET can be perpendicular to the Si substrates. In one embodiment, this can be different than the tunneling direction in the channel of lateral TFETs.