A new resonant tunneling diode (RTD) microwave oscillator operating at extremely low dc-power consumption is proposed, which utilizes the antiphase-coupled quantum-effect RTD oscillations for efficient ac-power generation at a summing node of output based on a push-push principle. The fabricated integrated circuit of the RTD microwave oscillator by using an InP-based RTD/HBT quantum-effect IC technology shows an extremely low total dc-power consumption of 85 ??W at an oscillation frequency of 29.1 GHz. In order to achieve the extremely low dc-power consumption, the device size of RTD has been scaled down to 0.7 ?? 0.7 ??m2. The obtained total dc-power consumption of 85 ??W at an applied bias of 0.49 V is found to be the lowest reported up to date, corresponding to about 1/170 of that in the conventional-type low-power oscillators in the related frequency range.