Mobile communication has evolved rapidly. Car phone service started in 1979, and mobile phone service started in the mid-1980s. Email and the Internet came into service in the first half of the 1990s and rapidly came into widespread use due to the release of smartphones in 2007. These developments were driven by wireless access technology.

Mobile communication has contributed significantly to improving the performance of mobile phones. The transmission system have evolved from first generation (1G) to fourth generation (4G) and recently, fifth generation, which achieves ultra-high-speed communication considered to be 100 times that of 4G, has emerged. Characterized by high-speed and large-capacity communication, low latency and simultaneous connectivity, 5G technology is expected to offer new service platforms beyond conventional mobile communication and to bring about various applications in society and daily lives. High-speed communication and large transmission capacity will enable live streaming of high-resolution videos and online home medical care, while low latency will dramatically advance Internet of Things (IoT) technology and a way of communicating with various things, including vehicles. Suppose you are driving at 60 km/h. When brakes are remotely applied to your vehicle, the braking distance using 4G is about 1.7 m, whereas the distance using 5G is only a few centimeters. Furthermore, simultaneous connectivity will achieve connections dozens of times more than those of 4G. Commercial 5G services have already been launched in 19 countries, including the U.S., South Korea and the U.K. in 2019. In Japan, 5G was launched in March 2020.

In 2005, the Sumitomo Electric Group became the first company in the world to market gallium nitride (GaN) high-electron-mobility transistors (HEMTs), which are extremely high-performance transistors. The presence of GaN HEMTs has been growing all the more with the advent of the era of 5G. GaN HEMTs have attracted much public attention around the world as electronic devices that underpin the 5G era. This feature focuses on the history of challenges to develop GaN HEMTs and the future outlook beyond the 5G technology.