The room temperature concentration and mobility of electrons introduced by Si-doped cubic GaN films have been derived from their Raman spectra. These films were grown by MBE on cubic SiC thin films deposited by CVD on Si. The Si-doped films has a mobility lower (in the 50 to 210 cm(2) V/s range) than (1650 cm(2) V/s) the undoped films, attributed to the significant increase upon doping of the hexagonal parasitic volume fraction in the films.