A high-power push-push transformer-based oscillator (TBO) adopting a capacitive degeneration technique is proposed. The capacitive degeneration circuit reduces the effective parasitic capacitances of the transistor and enhances the negative conductance generated by the TBO. The proposed oscillator is fabricated with 65-nm CMOS technology. The measured output power of the proposed single core oscillator is -1.4 dBm at 268 GHz with 2.4% dc-to-RF efficiency. The proposed oscillator core is able to generate a high output power at a high operating frequency while maintaining good dc-to-RF efficiency.