This paper presents a design for a 700 GHz signal source based on 130 nm indium phosphide (InP) heterojunction bipolar transistor (HBT) technology. The single element source, a push-push 350 GHz oscillator with a common-base cross-coupled topology, and frequency doubler with a balanced common-emitter topology requires no power combiner. The design exhibits superior frequency stability with changes to bias current, a peak output power of −11.8 dBm, phase noise of −73.8 dBc/Hz at 10 MHz offset, and dc-to-RF efficiency of 0.09%.