A high‐efficiency, resonant‐cavity, bipolar inversion channel field‐effect transistor detector is demonstrated with a triple‐strained InGaAs quantum‐well absorbing region. A quantum efficiency of 80% is obtained at a resonant wavelength of 0.94 &mgr;m, and a bandwidth of 20 A˚, giving a 26‐fold enhancement in absorption due to resonance. The transistor detector operates in the FET mode with an independent gate electrode to control its sensitivity, and in a bipolar mode with a photogain of 25. The structure is identical to that used in other inversion channel laser structures, and hence provides an optimum configuration for optoelectronic integration. This is the first demonstration of a three‐terminal quantum‐well resonant‐cavity photodetector.