A wide‐tuning range and ultra‐low‐phase‐noise 4.28‐GHz voltage controlled oscillator (VCO) is designed in this article. The VCO implemented with the TSMC 0.18 μm 1P6M CMOS technology uses NMOSs only. Source capacitive degeneration technique is used to increase the frequency tuning range. The proposed VCO can have an 18.94% tuning range from 3.53 to 4.34 GHz. The measured phase noise is −131.2 dBc/Hz at 1‐MHz offset from the 4.28 GHz. The corresponding figure‐of‐merit (FOM) and FOMT are calculated to be −191.6 and −197.15 dBc/Hz, respectively. The chip size is 0.571 × 0.822 mm2. The core circuit consumes 16.5‐mW and 1.3‐V power supply. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1941–1944, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26950