We report the operation of the first two‐dimensional electron gas (2‐DEG) emitter heterojunction bipolar transistor. This device, which was grown by molecular beam epitaxy, incorporates an undoped GaAs spacer between the emitter and base of a standard AlGaAs/GaAs single‐heterojunction bipolar transistor. The introduction of the spacer layer causes the formation of a 2‐DEG at the AlGaAs/GaAs interface. This 2‐DEG defines the emitter side of the junction and produces an emitter‐base characteristic similar to that of the collector GaAs homojunction. Using a 300 A˚ GaAs spacer, offset voltages as low as 30 mV have been attained. These devices also exhibit current gains greater than 10 at emitter current densities of 3 A/cm2and gains up to 400 in the high current density regime.