In some embodiments, an FET structure comprises a heterostructure, and a gate structure. The heterostructure comprises a first section, a barrier section and a second section such that a portion of the first section, the barrier section, and a portion of the second section form a channel region, and portions of the first section and the second section on opposite sides of the channel region form at least portions of source and drain regions, respectively. When the channel region is p type, the barrier section has a positive valence band offset with respect to each of the first section and the second section, or when the channel region is n type, the barrier section has a positive conduction band offset with respect to each of the first section and the second section. A gate structure is configured over the channel region.