A method for passive cancellation of substrate noise for a buck converter uses an on-chip capacitor to reduce the substrate noise. The capacitor achieves a close-magnitude noise with opposite phase for better noise cancellation effect in the substrate. The capacitor can be realized as a MOS capacitor, NMOS isolation ring n-well capacitor, n-well junction capacitor, isolated p-well junction capacitor, etc. The capacitor is easy to implement. Further, bond wire parasitic inductance in the buck converter is used to reduce substrate noise.