The electrical resistivity ρ, the Seebeck coefficient S and the carrier mobility µ were measured as a function of carrier concentration n for B- and P-doped Si, Si0.97Ge0.03 and Si0.95Ge0.05 prepared by arc melting. It was found that at a high carrier concentration of about 2×1020 cm-3, the S values of the Si0.97Ge0.03 and Si0.95Ge0.05 samples with dopant segregations are about 50% higher than those measured previously on Si0.95Ge0.05, Si0.85Ge0.15 and Si0.7Ge0.3 samples with little segregation, although the differences between their ρ values are very small. The most striking result is that the S curves of the doped Si samples have a hump at a concentration of about 3×1019 cm-3, while no hump was observed for the Si0.97Ge0.03 samples, as in the case of Si0.7Ge0.3 alloys. Such a hump is surprising because it conflicts with the conventional theory that predicts a monotonic decrease of S with increasing n. This phenomenon is related to a change in the effective mass which results from dopant segregation.