A GaAs monolithic voltage-controlled biphase attenuator and a vector synthesizer, which utilize remote-pinchoff cold field-effect transistors (RePOFET's), are newly developed for microwave signalprocessor applications. Their features are very small circuit size, which permits dense integration, and high control linearity. Lumped-constant topologies and internal impedance optimization successfully reduce the sizes of the attenuator and vector synthesizer to just 0.5 and 2.1 mm 2 , respectively. The control sensitivity deviation exhibited is within 65% for over 50% of the full control range. The uniformity of the measured vector constellation is also improved by the RePOFET's.