The recent increase in the number of communications systems required f
or both civil and military uses has led to interest in improving the s
emiconductor devices which lie at the heart of many transmitters and r
eceivers. This paper describes some recent advances in the area of sem
iconductor tunnelling devices, in which electrical conduction occurs p
rimarily by quantum-mechanical tunnelling. It discusses how such tunne
lling devices have some advantages over conventional devices for use i
n certain microwave communication systems.