We report on magnetotransport studies of Al0.15Ga0.85N/GaN high electron mobility transistor (HEMT) structures grown on p-type Si(111) substrates. Both weak localization (WL) and electron-electron interaction (EEI) correction terms to the conductivity of the SiN treated HEMT are smaller than those of the untreated HEMT. Since both WL and EEL corrections tend to decrease the conductivity of an AlGaN/GaN HEMT structure, our SiN treatment is useful for enhancing the performance of GaN-based HEMT structures grown on Si, which is compatible with the mature Silicon CMOS technology.