A fundamental W-band voltage-controlled oscillator (VCO) featuring high output power and wide tuning range has been successfully designed. The VCO was fabricated utilizing 0.8 μm InP DHBT technology. The DHBT exhibits peak fT of 170 GHz and fmax of 250 GHz. The VCO core implemented a balanced Colpitts-type topology modified for high-frequency application. An additional buffer amplifier stage was connected with the core to further boost output power as well as eliminate the load pulling effect. The DHBT base-collector P-N junction at reverse bias was chosen as a varactor diode to realize a wide frequency tuning. The measured results demonstrate that the oscillation frequency of the proposed VCO can be tuned between 81~97.3 GHz, which is a relative tuning bandwidth of 18.3 %. Over this frequency range the oscillator has a maximum output power of 10.2 dBm, and the power variation is less than 3.5 dB. A phase noise of -88 dBc/Hz@1MHz is obtained at the highest tuning frequency.