In this letter, an ON-OFF keying (OOK) oscillator that uses a resonant tunneling diode (RTD) pair configuration has been designed and fabricated. To achieve improved RF output power characteristics, the RTD pair topology was utilized in the RTD OOK oscillator design to realize an increased negative differential conductance voltage span. The fabricated IC showed high-speed switching capability of 5 Gb/s with a good phase noise characteristic of -118.17 dBc/Hz at a 1-MHz offset. The maximum RF output power was determined to be -1.76 dBm at a carrier frequency of 24.1 GHz. It consumes 12.5 mW of power, resulting in a good figure of merit value of 2.5 pJ/bit. These results demonstrate its potential as a high-performance ON-OFF mode oscillator for high-data-rate OOK transceiver systems.