A 40 GHz cross-coupled differential voltage controlled oscillator (VCO) is presented. To shorten the gap between the simulated and measured results in millimeter-wave circuits, the inductor and its extension metal line are simulated with 3D electromagnetic simulator. Thick gate varactor is utilized to widen the frequency tuning range. The VCO chip has been implemented in 65nm CMOS, and the measured results show that the chip achieves a tuning range of 12.2%, from 38.4 GHz to 43.4 GHz, which satisfies the frequency requirements of the 60GHz wireless transceiver with two stage down-conversion supporting IEEE 802.11ad. The simulated phase noise of the VCO from 39 GHz carrier is -98.2dBc/Hz at 1 MHz offset. The core of the VCO consumes 5.7mW to 8.6mW power from a 1.0 V power supply. The core die area is 0.197 ′ 0.436 mm2。