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A highly efficient voltage controlled oscillator (VCO) with a new varactor-less-based frequency-tuning topology for terahertz (THz) frequencies is presented. The tuning technique is based on a variable inductance seen at the emitter node of a base degenerated transistor. Fabricated in a 130nm SiGe BiCMOS process, the VCO achieves a tuning range of 3.5% and output power of -7.25 dBm at 201.5GHz. The VCO consumes 30mW of DC power, resulting in a record-breaking power efficiency of 0.6%. To demonstrate the functionality of the tuning technique, three other VCO prototypes at different oscillation frequencies, including one operating at 222.7~229 GHz range, have been implemented.