In this study, accuracy improvements in estimations of electrical properties of millimeter-wave devices were demonstrated using the probe-backside reflection method at frequencies up to 100 GHz. The dielectric properties of silicon wafers, with nominal resistivities from 1 Ωcm to 151 kΩcm, were preliminarily evaluated using the PBR method to determine the material parameters used in the electromagnetic simulation. The S-parameter of the mmW devices fabricated on the silicon wafers was calculated using the simulation. The calculated S-parameter was well accorded with the measured S-parameter of the devices fabricated on silicon wafers. The PBR method can provide more suitable material parameters than those calculated using the Drude model for resistive wafers with resistivities greater than 3 kΩcm. However, the accuracy was degraded compared to the Drude model in the most lossy 1–100 Ωcm wafer.