The potential of GaAs pHEMT technology for high-frequency power-switching applications is discussed within the context of integrated power supplies for portable wireless systems. Various technology considerations are presented, including the optimization of the power-switching transistor and passives integration. Two design examples for integrated dc-dc converters are implemented in a 0.5-μm GaAs E/D pHEMT process. The first uses coupled inductors to reduce the current ripple and enhance the dynamic performance of the converter. The two-phase, 0.5 A/phase converter occupies 2 mm × 2.1 mm without the output network. An 8.7-nH filter coupled inductor is implemented in 65-μm-thick top copper metal layer, and flip-chip bonded to the dc-dc converter board. The presented converter converts 4.5-V input to 3.3-V output at 150-MHz switching frequency with a measured power efficiency of 84%, which is one of the highest efficiencies reported to date for similar current/voltage ratings. The second example is a hysteric controlled, 100-MHz switching frequency single-phase GaAs pHEMT buck converter designed to drive power amplifier loads. The design can deliver up to 37-dB·m output power and has a peak efficiency of 88% and a 3-dB bandwidth of 14.5 MHz.