The room‐temperature photoinduced switching of an InGaAs/AlAs resonant‐tunneling diode is demonstrated. When illuminated at an irradiance of greater than 20 W cm−2 using 1.3 μm radiation, the resonant‐tunneling diode switches from a high‐conductance to a low‐conductance electrical state and exhibits a voltage swing of 600 mV. The switching characteristics are reversible and, in the absence of light, the detector returns to its original high conductance operating state. Small‐signal optical measurements performed with the device biased prior to resonance demonstrate a 3 dB bandwidth of ∼1.5 GHz.