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The responsivity to long wavelength (513 and 1253 μm) far-infrared (FIR) radiation and the root mean square noise voltage has been measured for one bulk GaAs and two GaAs/AlGaAs multiquantum-well (MQW) hot-electron photodetectors as a function of temperature from 4.49 to 77 K. From these data the noise-equivalent power (NEP) was determined for each device over the same temperature range. The MQW detectors were measured to have 77 K responsivities and NEPs that were one to two orders of magnitude better than those measured using the high purity bulk GaAs sample. To the best of our knowledge, these are the first measurements which show that hot electron MQW detectors are able to outperform bulk GaAs detectors at 77 K. Furthermore, the photoresponse of the MQW structures showed a much slower temperature dependent rolloff as compared to the bulk device, which implies a potential for applications at temperatures above 77 K. Detection of nanosecond pulses of 496 μm FIR radiation by one MQW detector and the bulk GaAs is additional evidence of hot-electron photoconductivity. © 1998 American Vacuum Society.