Recent advances in GaN power switching devices are reviewed. A new normall-off GaN transistor called Gate Injection Transistor (GIT) increases drain current by conductivity modulation. The GIT is fabricated on cost-effective Si substrates by novel MOCVD technology enabling crack-free and smooth surfaces over 6-inch wafer. These technologies with thermally stable device isolation by Fe ion implantation are applied for a monolithic inverter IC. This is the world fist demonstration of a GaN inverter IC for motor drive, which reduces the total operating loss by 42% from that by the IGBT-based inverter. These technologies are indispensable for wide-spread use of GaN power switching transistors in the future.