A Ku-band gm-boosting differential Colpitts voltage controlled oscillator (VCO) is presented, that relaxes oscillation start-up current requirement in Colpitts oscillator. Experimental results from a 0.18-μm CMOS process validate the gm-boosting design principle. The VCO oscillates at the frequency of 13.725 GHz with 6% tuning range. The current dissipation of the VCO is 4.5 mA from a 0.9 V power supply. The measurements at 13.3 GHz show the phase noise of -84.8 and -113.8 dBc/Hz at 100 kHz and 1 MHz offset, respectively. The calculated figure of merit (FOM) of this VCO is high as -190.2 dB. The chip size including test pads is 0.62 × 0.72 mm2.