A self-mixing wide tuning range voltage-controlled oscillator (VCO), using 0.35 μm SiGe bipolar technology, is proposed in this work. The entire circuit consists of a VCO core, a mixer and an emitter coupled differential amplifier. The fundamental and second harmonic signals from the VCO core are used as LO and RF input signals for the mixer circuit, respectively. The mixing product at the third harmonic of the VCO core is selected and amplified, while the low frequency part of the mixing product is suppressed. The simulated harmonic suppression of the third harmonic over fundamental signal is higher than 18 dB. The VCO operates from 91 to 101 GHz with 10.6% tuning range. The measured phase noise at 3 MHz offset is lower than -83 dBc/Hz over the entire frequency band. The VCO occupies 700 × 500 μm2 die area and consumes 185 mW under 3.5 V dc power supply.