Millimetre-wave and sub-millimetre-wave applications, such as satellite communications, radar systems, high-speed wireless communications, and newly developed mobile 5G system, have demanded high power and high effciency devices. GaN device is still a main player for the above frequencies and applications. This workshop will introduce the recent progress in GaN technology in millimetre-wave applications. This workshop will provide the bridge between a system/circuit designer and a device engineer. The workshop will start discussing the required performances for recent millimetre-wave applications including 5G system. After that, the workshop will cover the recent developed GaN devices for millimetre-wave and submillimetre-wave operation, device simulation, device modelling, and PA design techniques. This proposed workshop is endorsed by IEEE MTT-S TC-7.