AmonolithicAlGaN/GaN HEMT voltage-controlled oscillator has been designed, fabricated and characterized. The oscillator design utilizes a common-gate negative resistance topol-ogy with a multi-finger interdigitated Schottky diode varactor resonator for frequency control. The VCO operating at 15V drain bias and -4 V gate bias, exhibits frequency range between 8.5 and 9.5 GHz with maximum output power of 31.8 dBm across a 50ohmload. Maximum power variation does not exceed ±0.8 dB in the oscillation frequency band. Average phase noise in the bandwith is estimated to be equal to -77 dBc/Hz at 100 kHz offset and -101 dBc/Hz at 1 MHz offset. Average tuning sensitivity is measured to be 120 MHz/V. Oscillator’s pulling figure is equal to 139 MHz for 12 dB return loss. Pushing figure is 114 MHz/V. Output power can be increased up to 35 dBm (2.1 W/mm) by setting drain bias voltage at 30 V.