Quenched multiple domain (q.m.d.) mode oscillations in bulk GaAs have been analysed to obtain the relationships between efficiency, fundamental-frequency power output, fundamental-frequency negative resistance, and d.c. bias voltage. It is found that this highly efficient mode does not have the limitations of transit-time devices and consequently has a frequency-independent power × impedance product. The results demonstrate that q.m.d. oscillators designed with multiple-tuned circuits can operate at twice the efficiency of those operated in single-tuned circuits.