This paper proposes a dc-voltage equalizing circuit for a diode-clamped linear amplifier (DCLA). The DCLA consists of series-connected complementary MOSFETs and diode clamping circuits, which has an experimental efficiency as high as 90% without switching operation. The DCLA requires a dc-voltage equalizing circuit to divide the dc voltage into several levels. The proposed dc-voltage equalizing circuit enables to use a diode rectifier with a smoothing capacitor as a power supply for the DCLA. Moreover, zero-sequence voltage control is proposed to improve efficiency of the DCLA. As a result, a prototype twelve-series DCLA demonstrates an experimental efficiency as high as 94.7%.