The subject embodiments relate to carbon nanotube (CNT) transistors with carrier blocking using thin dielectric under the drain or source and drain contacts. According to an embodiment, a transistor is provided that comprises a CNT channel layer, a metal source contact formed on the carbon nanotube channel layer, and a metal drain contact formed on the carbon nanotube channel layer. The transistor structure further comprises a drain dielectric layer formed adjacent to and between a lower surface of the metal drain contact and an upper surface of the carbon nanotube channel layer. In one or more implementations, the drain dielectric layer comprises a material that suppresses injection of a first type of carrier into the CNT channel layer and facilitates the injection of a second type of carrier into the CNT channel layer.