A miniaturized K-band VCO (voltage controlled oscillator) using GaAs pHEMT device is presented. A compact mushroom-type edge-located vias electromagnetic bandgap (ELV-EBG) resonator loaded with a varactor is adopted instead of conventional resonator. The parallel feedback structure VCO is designed to operate from 22.9 GHz to 25.6 GHz. The measured results show that the proposed VCO provides a maximum output power of 10.4 dBm at 23.6 GHz with output power flatness less than 1 dB from 24 GHz to 25.4 GHz. The phase noise of the VCO with ELV-EBG resonator is around ?95 dBc/Hz at 1 MHz offset from carrier. The size of this compact VCO is about 17 mm×7.5 mm.