3 W CW simultaneously with 22% conversion efficiency was achieved at 35 GHz from a double-drift GaAs IMPATT diode. At 44 GHz, 2 W and 18% efficiency were obtained. The design of the amplifier circuits which utilize these devices is discussed. The circuit design is based on a 3-step closed form algorithm. The first step is a passive circuit characterization with automatic network analyzer. In the second step a computer is used to generate diode device lines, and the third step is load line synthesis for predictable operation. The resulting performance and its sensitivity on the mechanical tolerances is described. 2 W over a 2-GHz bandwidth was achieved simultaneously with minimum gain of 9 dB.