In this paper, we discuss the design and measurement results of a very broadband and efficient millimeter-wave (mm-Wave) medium-power power amplifier (PA) for potential mm-Wave 5G applications. This PA is designed in an advanced mm-Wave 22 nm CMOS FD-SOI technology and targets to cover most of the key 5G FR2 band (e.g., from 24.25 to 43.5 GHz). This PA achieves an outstanding 3-dB bandwidth (BW) of 19.1 – 46.5 GHz, while maintaining >12.5% max. PAE (power-added-efficiency) across the entire 27.4 GHz BW with a max. PAE of 26.1% at 24 GHz. The linearity of this PA is also tested with 50/100/400/9x100 MHz 256-QAM 5G NR signals (PAPR or peak-to-average-power-ratio = 8 dB), which demonstrates useful insights on CMOS PA linearity degradation with increasing BW. We will also compare our PAs’ performance vs. other state-of-the-art silicon broadband mm-Wave PAs in the literature.