Abstract: In this study, we demonstrated the InP-based Gunn diode for W-band waveguide oscillator application. The fabricated InP-based Gunn diode has a Stable Depletion Layer (SDL) nn+ structure for low operating currents, high output power and high dc-to-RF conversion efficiency. The 94 GHz waveguide oscillator was also developed in order to demonstrate the RF characteristics of the packaged InP-based Gunn diode. When the anode diameter of InP-based Gunn diode was 60 μm, typical values of oscillation frequency and output power were 94.25 GHz and 16.11 dBm with a dc-to-RF conversion efficiency of 1.6%, respectively, at dc bias of 9 V. The highest output power of 19.1 dBm was obtained with a dc-to-RF conversion efficiency of 2.5% at dc bias of 11 V. The measured phase noise was <-102.9 dBc/Hz at 1 MHz offset with 10 kHz of resolution bandwidth.