A Ka‐band substrate integrated waveguide (SIW) voltage‐controlled oscillator (VCO) is demonstrated using GaAs Gunn diode.GaAs hyperabrupt varactor is employed in parallel to the Gunn diode for low phase noise and wideband tuning. The VCO achieves a tuning range of more than 1 GHz by varying the varactor tuning voltage between 0 V and 9 V, and phase noise of −102.1 dBc/Hz at 1 MHz offset from a 36 GHz carrier frequency. The output power varies from 9.3 dBm to 11.3 dBm within the tuning range. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1232–1235, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25169