Aggressively scaled gallium nitride (GaN) high-electron-mobility transistor (HEMT) technologies with 40 nm T-gate lengths and extremely scaled ohmic-regrowth source-drain lengths ranging from 1500 nm to 150 nm comprise the low-loss, high-performance active devices in advanced high-power and high-efficiency monolithic microwave integrated circuits (MMICs). This paper outlines the latest device, circuit, and foundry access of three commercially available 40 nm GaN T-gate MMIC processes for millimeter-wave applications.