This article presents a high-power wideband power amplifier (PA) with a four-way power-combining technique for D -band high-resolution radar. The power combiner is based on a two-section Chebyshev impedance converter to achieve a large bandwidth (BW) and is realized with slow wave coplanar waveguides (S-CPWs) to reduce the insertion loss and chip area. Therefore, our developed technique can provide broadband and low-loss power-combining scheme in a very compact size. A high-power PA with four-way combining has been fabricated in a 28-nm CMOS bulk technology. The unit PA uses low- k transformer-based coupled-resonator networks to realize wideband matching. The measured results of the PA prototype demonstrate the peak gain of 22.6 dB, the saturated output power of 16.2 dBm, and the peak power added efficiency of 8.6% at 135 GHz with a 3-dB BW of 28 GHz from 124 to 152 GHz. Meanwhile, the total area of this PA die is merely 0.66 × 0.73 mm.