A resonant tunneling diode (RTD)-based microwave on-off mode oscillator for on-off keying (OOK) transceiver applications operating at extremely low power consumption is proposed. In order to achieve the low-power operation, the negative differential conductance characteristic at a low-voltage arising from quantum effects of the RTD is used for RF signal generation. The fabricated integrated circuit of the RTD-based oscillator by using an InP-based RTD/heterojunction bipolar transistors quantum-effect IC technology shows low power consumption of 1.14 mW at an oscillation frequency of 5.725 GHz industrial, scientific, and medical band. The fabricated RTD-based oscillator operates in an on-off mode with a high data rate of 500 Mb/s. The obtained energy efficiency of 2.28 pJ/bit is found to be the best reported up to date.