An S/C-band SiGe HBT differential VCO has been developed for the next generation wireless radios. It employs a novel HPF-type resonator having a parallel LC circuit in place of the conventional series capacitance to achieve a higher oscillation frequency. This resonator can be constructed from only the chip inductors with the use of their parasitic capacitance to achieve a miniaturized size. The differential oscillator, which employs a novel HPF-type resonator with triple 1005-type 1nH chip inductors and 0.35μm SiGe HBTs with an ft of 25GHz, has achieved an oscillation frequency of 4.21GHz, an output power of -16.5dBm, a current of 2.67mA, and a phase noise of -104dBc/Hz at 100kHz offset for a VCC of 3V. As compared with the case using the conventional HPF-type resonator, the oscillation frequency becomes around 0.91GHz higher. The differential VCO, which employs a Si varactor diode with a capacitance ratio of 2.5, has achieved an oscillation from 3.36 to 4.03GHz, an output power of greater than -16.8dBm, a current of less than 2.93mA, and a phase noise of less than -100dBc/Hz at 100kHz offset for a VCC of 3V. This is the first report on the differential VCO using only chip inductors as a resonator element.