This paper presents the Monte Carlo studies of inversion mobility in Ge MOSFETs covering a wide range of bulk-impurity concentrations (10(14) cm(-3)-10(17) cm(-3)), and substrate bias (0-10 V). Carrier mobilities in Ge MOSFETs have obviously increased compared with those in Si MOSFETs. At low effective field, both electron and hole mobilities have increased over 100%; while at high effective field the increase is reduced due to the effect of surface roughness. Similar to Si MOSFETs, the carrier effective mobilities in Ge MOSFETs also have a universal behavior. The universality of both electron and hole mobilities holds up to a bulk-impurity concentration of 10(17) cm(-3). On substrates with higher bulk-impurity concentrations, the carrier effective mobilities significantly deviate from the universal curves under low effective field because of Coulomb scattering by the bulk impurity. (C) 2005 Elsevier Ltd. All rights reserved.