The errors produced in a Hall-effect multiplier are examined and shown to belong to one of two categories: either they are due to coupling between input or output, or they are produced by non-linear processes within the device. An estimate of the magnitude of the errors is given and interpreted in terms of carrier leak, modulation leak and envelope distortion for the particular application of a Hall-effect modulator. A comparison is made between plates constructed of indium antimonide and indium arsenide on the bases of carrier suppression, temperature stability, conversion efficiency and distortion. Carrier suppressions of up to 80 dB can be obtained for both materials.