The design and performance of the LSA-BC, a novel power amplifier, are presented. A linear amplifier with the high efficiency of a switching-mode saturation amplifier can be realized. A high-efficiency GaAs FET is roughly linearized by dynamically varying its drain DC voltage with a high-efficiency variable-output DC-DC converter. A negative envelope feedback is utilized to compensate for the residual. The circuit construction is simple enough for use in the portable subscriber units of a digital mobile radio system. A 1.5-GHz-band 1-W LSA-BC was constructed to determine its performance with 32-kb/s roll-off QPSK (quadrature phase-shift keying). As a result, a 40% total efficiency is achieved as well as a stable third-order intermodulation distortion of -50 dB to the signal level.