In this paper, we show through both calculations and Hall effect measurements that incomplete ionization of dopants has a greater influence on the majority-carrier density in p-type and n-type compensated Si than in uncompensated Si with the same net doping. The factors influencing incomplete ionization at room temperature are shown to be the majority-dopant concentration, its ionization energy and type, and the compensation level. We show that both the majority-and the minority-carrier mobilities are lower in compensated Si than expected by Klaassen's model and that the discrepancy increases with the compensation level at room temperature. The study of the temperature dependence of the majority-carrier mobility shows that there is no compensationspecific mechanism and that the reduction of the screening in compensated Si cannot explain alone the observed gap between experimental and theoretical mobility.