Three‐terminal real‐space transfer devices have been implemented in InGaAs/InAlAs/InGaAs heterostructure material. The use of nonalloyed contacts provides excellent ohmic contacts to the channel without compromising insulation from the second conducting layer, The observed negative differential resistance has a peak‐to‐valley ratio that typically exceeds 100, both at room temperature and cryogenic temperatures. The highest observed peak‐to‐valley ratio at 300 K was 490. With increasing heating voltage, the injection current across the InAlAs barrier rises in a sequence of sharp steps. We explain this feature by an instability caused by a positive feedback between the heating field in the channel and the local real‐space transfer current.