This paper presents a millimeter-wave wide tuning range voltage-controlled oscillator (VCO) incorporating two switchable decoupled VCO cores. When the first core is switched on producing the low frequency band (LFB) signal and the second core is off, the inductors of the second core are reused to create additional buffers that pass the LFB signal to the output buffers. The generated high frequency band (HFB) signals by the second core when turned on, are directly fed to the output buffers. Producing the outputs of both VCO cores across same terminals without utilizing active/passive combiners and coupled inductors will enhance the phase noise performance of the VCO, increase its output power, and reduce the chip size. Fabricated in a 65-nm CMOS process, the VCO achieves a measured wide tuning range of 26.2% from 54.1 to 70.4 GHz while consuming 7.4-11.2-mA current from 1-V power supply. The peak measured phase noise at 10-MHz offset is -116.3 dBc/Hz and the corresponding FOMT and FOM varies from -180.96 to -191.86 dB and -172.6 to -183.5 dB, respectively. The VCO core area occupies only 0.1 ×0.395 μm².