Some narrow‐gap mixed crystal semiconductors show a magnetic field induced transport anomaly at low temperatures. The anomaly is accompanied by a transition from a low to a high resistivity state, which in turn causes a strongly nonlinearI‐Vcharacteristic. We have investigated microwave mixing near such a phase transition inn‐type Hg0.8Cd0.2Te with a frequency of 37 GHz at 1.5 K and in magnetic fields up to 8.5 T. The sensitivity characteristic was measured and the responsivity determined to be about 15 times higher than that of a hot‐carrier InSb bolometer. The time resolution of this new bolometer (=10−7s) was slightly better than in InSb.