This letter presents a resonant tunneling diode (RTD)-based differential oscillator topology which can enhance output power coupling for THz applications. In order to combine the differential output signals of the RTD differential oscillator, an on-chip dipole antenna is integrated into the InP-based RTD monolithic microwave integrated circuit technology. The fabricated RTD differential oscillator shows a radiated output power of 47 mu W with a total dc power consumption of 14.1 mW at an oscillation frequency of 675 GHz. A high dc-to-RF efficiency of 0.33% has been obtained. This is the first implementation as an RTD differential oscillator topology for THz sources, integrated with the on-chip dipole antenna.