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This paper presents efficiency optimization of X-band two-stage microwave power amplifiers (PAs) in which the output stage is designed to operate in class-E mode. A hybrid PA which uses the same MESFET devices in both stages achieves 16 dB of saturated gain with an output power of 20 dBm and total power added efficiency (PAE) of 52% at 10 GHz. A broadband monolithic two-stage double heterojunction bipolar transistor PA, fabricated by Northrop Grumman Space Technology, with a class-AB first stage and class-E second stage achieves 24.6 dBm of output power with 24.6-dB gain and total PAE of 52% at 8 GHz. The design is performed starting from class-E theory and using load-pull measurements and/or nonlinear simulations.