SiO2/InAlN interfaces formed by plasma‐enhanced chemical vapor deposition were investigated. X‐ray photoelectron spectroscopy showed that the direct deposition of SiO2 onto an InAlN surface led to the oxidation of the InAlN surface. The interface state density, Dit, was on the order of 1012 cm−2 eV−1 (5 × 1012 cm−2 eV−1 at 0.3 eV from the conduction band edge, Ec), which indicated the possibility of improving the interface properties. Reduction of the interface state density was attempted using an Al2O3 interlayer and a plasma oxide interlayer. The insertion of a 2‐nm‐thick Al2O3 interlayer to prevent surface oxidation by plasma reduced Dit slightly. A marked reduction in Dit to less than 1011 cm−2 eV−1 deeper than 0.3 eV from Ec, however, was achieved by the intentional formation of a 1‐nm‐thick plasma oxide layer, formed by N2O plasma oxidation, as an interlayer between SiO2 and InAlN.