In this work, experimental data is presented on the heterostructure hot electron diode (H 2ED), a two-terminal device that exhibits S-shaped negative differential resistance due to a field dependent transition between the current conduction modes of tunneling and thermionic emission of hot electrons in a two-layer AlGaAs heterostructure. Results are presented on various single and multiple period H 2ED structures fabricated from wafers grown by metalorganic chemical vapor deposition (MOCVD). Preliminary microwave characterization of the H 2ED on non-optimized structures have resulted in test-fixture-limited oscillation at frequencies greater than 17GHz.