This paper presents an ultra-wideband voltage controlled oscillator (VCO) IC using 0.35 μm SiGe BiCMOS technology. The VCO IC exhibits an oscillation frequency from 2.67 to 4.37 GHz. To realize the wideband tuning range, a novel resonant circuit is proposed. The novel resonant circuit consists of three NMOS varactor pairs, p-n diodes, two spiral inductors and a control circuit which sequentially applies a control voltage to the NMOS varactor pairs and p-n diode pairs. The novel resonant circuit allows the VCO IC to have the wideband tuning range with a single analog control voltage. The dc current consumption of the VCO is 5.8 mA at a collector voltage of 4.0 V. The VCO has a phase noise of -111 dBc/Hz at 1 MHz offset at an oscillation frequnecy of 4.37 GHz.