This paper presents a high efficiency, high switching speed, two-stage interleaved DC-DC buck converter with negatively-coupled inductors in AlGaAs/GaAs technology, targeting integrated power amplifier modules. The flip chip DC-DC converter is implemented in 0.5 μm GaAs pHEMT process and occupies 2 × 2.1mm2 without the output network. The inductors in the output network are implemented in 65 μm thick top copper metal layer and have a quality factor of 25 at 150 MHz. The interleaved DC-DC converter achieves 84% efficiency when operating at 150MHz switching frequency with 4.5V/3.3V conversion ratio and 1A load current.