In this paper, a novel on-interposer passive equalizer is proposed for chip-to-chip high-speed data transmission on the silicon-based on-interposer channel. The proposed equalizer uses the parasitic resistance and inductance of the on-interposer shunt metal lines to produce the high-pass filter. This filter enables the proposed equalizer to exhibit wideband channel equalization and low power-consumption. Based on the equivalent-circuit model of the proposed on-interposer passive equalizer, the physical dimensions of the equalizer are optimized for 30-Gb/s serial data transmission. The performance of the proposed equalizer with the optimized dimensions was successfully demonstrated by both frequency-and time-domain measurements at data rates of up to 30 Gb/s. In addition, a compact on-interposer passive equalizer was designed for the wide I/O interposer using the same mechanism. The improved quality of serial data transmission in the equalized wide I/O on-interposer channel was successfully verified by simulations at data rates of up to 10 Gb/s.