The paper describes the theory and performance of a new microwave mixer based on the fact that the Hall electric field produced at any point in a semiconductor is dependent on the vector product of the current density and the magnetic field applied at that point. This mixer stage behaves differently from the more conventional forms in that the output contains only components of the local-oscillator and signal frequencies.Two designs of Hall-effect mixer were developed, and their conversion properties were experimentally investigated at about 10Gc/s. The best value achieved for the conversion loss was 57 dB with a local oscillator power of 10W and using a semiconducting film of indium antimonide having a Hall mobility of 0.173m/s per V/m. It should be possible to improve the efficiency of this mixer by using higher-mobility films and higher power for the local oscillator, and by operating the device at low temperatures.Besides being a linear device, the Hall-effect mixer has a power-handling capacity which is much larger than that of the ordinary crystal mixer. Moreover, the technique used offers a useful method for measuring the Hall mobilities of carriers in semiconductors at microwave frequencies.New information is also given about a technique for the preparation of evaporated indium-antimonide films which proved to have a Hall mobility as high as one-fifth of the material in bulk.