This paper presents a pseudodifferential power amplifier for 77-GHz automotive radar. The circuit is fabricated in a SiGe HBT BiCMOS technology featuring bipolar transistors with fT/fmax of 230/280 GHz. The amplifier adopts a transformer-coupling current-reuse approach to improve both gain and efficiency. An interstacked transformer is also profitably adopted to reduce output losses due to the differential-to-single-ended conversion. The amplifier exhibits a saturated power, a peak power-added efficiency, and a gain of 14.5 dBm, 9%, and 25 dB, respectively, thus achieving a first-rate figure-of-merit as high as 4755.