A new fully integrated, dual‐band CMOS voltage controlled oscillator (VCO) is presented. The VCO is composed of two complementary Colpitts VCOs and is implemented in 0.18‐μm CMOS technology with 2‐V supply voltage. The circuit allows the VCO to operate at two resonant frequencies with a common LC tank. This VCO is configured with 2.4‐ and 5.2‐GHz frequency bands with differential outputs. The dual‐band VCO operates at 2.39–2.68 GHz and 4.84–5.58 GHz. The phase noises of the VCO operating at 2.4 and 5.13 GHz are −121.11 and −111.76 dBc/Hz at 1‐MHz offset, respectively, while the VCO draws 7.45/5.92 mA and 14.9/11.84 mW consumption at high/low frequency band from a 2‐V supply. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2634–2637, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22814