In addition to high power, power amplifiers for 5G mm-wave systems typically require high efficiency at 8dB back off and linearity appropriate for wideband 64 QAM OFDM signals without digital predistortion. This presentation discusses techniques for achieving these objectives using both single amplifiers and Doherty-combined amplifiers. Results are shown for 28GHz CMOS-SOI PAs based on nMOS and on pMOS (to increase voltage handling capability).