Optimal voltage-controlled oscillator (VCO) design for ultralow-power (ULP) radios has to fulfill simultaneously multiple requirements such as frequency tuning range, phase noise, power consumption, and frequency pushing. The manual design struggles to approach the full potential that a given topology can achieve. In this work, we prove the role of electronic design automation (EDA) tools by fully supporting the complex design of a ULP complementary Class-B/C hybrid-mode VCO. In the 1 st step of the EDA-assisted flow, we perform a worst-case corner of worst-case tuning sizing optimization over a 108-dimensional performance space, offering sizing solutions with power consumption down to 145 μW at the worst-case. In the 2 nd step, we introduce an automatic layout generation tool to offer valuable insights into the post-layout design space and devise a ready-for-tape-out fine optimization strategy. The hybrid-mode VCO prototyped in 65-nm CMOS occupies a die area of 0.165 mm 2 and dissipates 297 μW from a 0.8 V supply at 5.1 GHz. The phase noise at 1 MHz offset is −110.1 dBc/Hz, resulting in a competitive Figure-of-Merit (FoM) of 189.4 dBc/Hz well-suited for ULP applications.