rdquoWe report the first submillimeter-wave monolithic microwave integrated circuit (MMIC) amplifier with 4.4-dB measured gain at 308-GHz frequency, making it the highest frequency MMIC amplifier reported to date. In this letter, a 35-nm InP high-electron mobility transistor process has been successfully developed with a projected maximum available gain of greater than 7 dB at 300 GHz. The excellent dc and RF performance makes it suitable for applications at frequencies well into the millimeter-wave band and, for the first time, in the submillimeter- wave band as well.