The dispersion characteristics of an MIS (metal-insulator-semiconductor) transmission line are studied using a spectral-domain integral-equation approach. The semiconductor is characterized by a conductivity that is pertinent to the majority carrier concentration of the semiconductor, and the depletion region is modeled as a lossless dielectric. It is found that for a lightly doped semiconductor, the slow-wave factors computed with and without the depletion region are close to each other, while the attenuation constants are somewhat different in the slow-wave region. For a more heavily doped semiconductor, the presence of the depletion region, although thinner than the lightly doped case, has a much stronger impact on both the slow-wave factors and the attenuation constants.