ABSTRACT A novel complementary ClassF 23 voltage‐controlled oscillator (VCO) is proposed. The design employs a transformer‐based tank and integrates two additional LC tanks that provide resonance at the third harmonic frequency. This harmonic superposition enables a sharp zero‐crossing region, which minimizes the effective Impulse Sensitivity Function (ISF), and consequently further improves phase noise (PN). Simulation results show that the additional third harmonic resonance contributes to a 1.4 dB reduction in phase noise compared with a standard Class F −1 oscillator. Fabricated in a 180 nm CMOS process, the prototype VCO occupies an area of 0.88 × 1 mm 2 . Measurement results show a tuning range of 4.26–4.58 GHz. The PN at 1 MHz offset is −126 dBc/Hz from the 4.26 GHz carrier frequency, with an average PN better than −120 dBc/Hz across the entire tuning range. A figure‐of‐merit (FoM) of 190.6 dBc/Hz is obtained at the 1 MHz offset. Under a 1.8 V supply voltage, the proposed design consumes a power of 6.2 mW.