Sophisticated communication and radar systems in the submillimetre wavelength bands will only be realised when the designers have access to the same diversity of devices available at lower frequencies such as circulators, differential phase shifters and nonreciprocal isolators. Below 100 GHz these devices depend on high quality ferrites. However, despite considerable investment in research and development, ferrites materials have not been realised that will yield acceptable performance at higher frequencies. This prompted the author to start investigating the possibility of using surface magnetoplasmons on high quality lightly doped semiconducting substrates as the vehicle for the design of nonreciprocal components in the submillimetre regime. This paper chronicles investigations pursued during the period 1976–1986, principally by faculty and students at Brown University and Lehigh University, into the behaviour of surface magnetoplasmons in a variety of canonical structures germane to nonreciprocal devices in the millimetre and submillimetre wavelength ranges. Interest focused on performance characteristics for such devices as differential phase shifters and nonreciprocal isolators. Critical to obtaining acceptable performance parameters such as insertion loss are, of course, the loss characteristics of the semiconducting materials. The latest results, based on studies of our canonical device models and presuming the use of the best available materials, indicate that acceptable device performance should be attainable. Results are presented that show insertion loss as well as isolation ratio for representative nonreciprocal isolator structures and the attained differential phase shift per unit insertion loss for a canonical differential phase shift configuration.