We propose a novel frequency doubler, implemented in three terminal semiconductor heterostructures. This device represents a natural embodiment of the symmetry of hot-electron injection with respect to the polarity of the heating voltage. An efficient frequency doubling, comprising conversion gain with low harmonic distortion of the output signal was demonstrated using InGaAs/InAlGaAs/InGaAs charge injection transistor devices. A natural extension of this idea is the implementation of a higher order frequency multiplier and a frequency mixer.