New high power (CW) at X-band from GaAs Schottky-barrier diodes was achieved as a result of improved heat sink and Schottky-barrier contact formation techniques. An output power of 2.1 watts (CW) at 9.2 GHz with an efficiency of 9 percent was obtained from a diode mounted on a diamond heat sink with the Schottky-barrier contact adjacent to it. The measured thermal resistance was about 7°C/W. The diodes were fabricated using platinum and molybdenum on n-type epitaxial GaAs substrate.