A high-power subterahertz (THz) push-push oscillator topology is proposed. Adopting Hartley oscillator topology with transformer as its resonator, the proposed oscillator reduces the effective parasitic capacitance of transistors; therefore, a larger size transistor can be adopted, which increases the output power while still maintaining the same oscillation frequency. The adoption of the transformer also improves the LC resonator's Q-factor, further improving the output power and dc-to-RF efficiency. Implemented in 65-nm CMOS technology, the measured output power of the proposed single oscillator is 2.3 dBm at 264 GHz with 2.76% dc-to-RF efficiency and -96.8 dBc/Hz of the phase noise at a 10-MHz offset.