A low-phase-noise wide-tuning-range K-band voltage-controlled oscillator (VCO) is presented in this paper. By employing accumulation MOS (AMOS) varactors deposited between drain and source terminations of the cross-coupled pair, the tuning mechanism are enhanced, leading to a boosted VCO tuning range. Moreover, the phase noise can be improved due to the better cyclostationary noise property. Based on this architecture, the fabricated VCO in 0.18-µm CMOS exhibits a measured 18.2% tuning range. Operating at 0.6-V supply voltage, the VCO consumes 2.28-mW dc power excluding the buffers. The measured phase noise is -112.53dBc/Hz at 1-MHz offset from 24.68-GHz oscillation frequency. Compared to the recently published K-band 0.18-µm CMOS VCOs, it is observed that the proposed VCO can simultaneously achieve low phase noise, wide tuning range, and low dc-power dissipation.