This paper presents a series-LC-assisted oscillator. By utilizing the series LC, the tank impedance at the oscillation frequency is significantly reduced compared to the conventional parallel LC tank, which contributes to reducing the phase noise (PN). Additionally, large-size cross-coupled transistors should be utilized to maintain the oscillation due to the low tank impedance. This induces a large parasitic capacitance that limits the frequency tuning range (FTR) at high frequencies in the conventional cross coupled oscillator. In contrast, the presented oscillator can operate above 10 GHz with a sufficient FTR, thanks to the capacitance boosting capability of the series LC. Fabricated in a 65 nm CMOS process, the oscillator achieves a PN of -140.2 dBc/Hz at 10 MHz offset from a 10.7 GHz carrier, consuming a power consumption of 21 mW, resulting in a figure of merit (FoM) of 187.5 dBc/Hz.