A new multiquantum well hot‐electron microwave detector is demonstrated. The GaAs–AlGaAs heterostructure was grown by molecular beam epitaxy and tested in theXandKbands. It showed room‐temperature operation with responsivity of several 103 V/W. The operation of the device is based on enhanced thermionic current due to carrier heating by the incident in‐plane polarized microwave electric field. This principle yields a broad frequency range of operation extending up to the millimeter band without significant degradation of the responsivity. ©1995 American Institute of Physics.