This brief discusses the impact of twin- and triple-well structures on power supply noise, and a substrate model for simulating the power supply noise. We observed noise reduction by the resistive network of the p-substrate and noise reduction by the junction capacitance of a triple-well structure on a 90-nm test chip. Measurement results also showed that the total noise reduction of a triple-well structure is superior to that of a twin-well structure. The measurement results correlate well with the results obtained from the power supply noise simulation using a hierarchical resistive mesh model. Our simulation-based verification indicates that in common CMOS design, a triple-well structure can reduce the power supply drop by 10%–40% or the decoupling capacitance area by 5%–10%. We also verified that supply drop sensitivity to variation of the well junction capacitance is sufficiently small and that supply noise reduction using a triple-well structure is robust to process variation.