The net doping characteristics of Si-doped n-GaN grown on Si(111) substrate and on c-sapphire substrate by MOVPE were investigated. In case the carrier concentration is less than 1 x 10(17) cm(-3), the n-GaN on Si has a strong compensation behavior. But it seems that it does not depend on carbon concentration as p-type dopant, but on other acceptors associated with crystal defects. AlGaN/GaN HEMTs were fabricated on both substrates. DC performance of the devices fabricated on Si substrate is in no way inferior to that of devices grown on sapphire substrate. (C) 2008 Elsevier B.V. All rights reserved.