The electrical properties of electron beam (EB) evaporated silicon dioxide(SiO2)/n-GaN,plasma enhanced chemical vapor deposited (PECVD)SiO2/n-GaN,and PECVD silicon nitride(Si3N4)/n-GaNinterfaces were investigated using high frequency capacitance–voltage measurements. Compositions of the deposited insulating layers(SiO2andSi3N4)were analyzed using x-ray photoelectron spectroscopy. Metal-insulator-semiconductor structures were fabricated on the metalorganic chemical vapor deposition grownn-type GaN layers using EB, PECVD grownSiO2and PECVD grownSi3N4layers. Minimum interface state density(2.5×1011 eV−1 cm−2)has been observed in the PECVD grownSiO2/n-GaNinterface when it was compared with EB evaporatedSiO2/n-GaNinterface(5.3×1011 eV−1 cm−2)and PECVDSi3N4/n-GaNinterface(6.5×1011 eV−1 cm−2).The interface state density(Nf)depends on the composition of deposited insulating layers. ©1998 American Institute of Physics.