Three-terminal GaAs/InGaAs/GaAs pseudomorphic real-space transfer heterostructure employing graded channel as the emitter layer grown by low-pressure metal-organic chemical-vapor deposition has been fabricated. We observe controllable drain cut-in voltage characteristics with strong negative differential resistance. The largest peak-to-valley current ratio of the proposed device is about 33 000 at room temperature. Moreover, we observe an energy exchange effect between electrons. ©1997 American Institute of Physics.