A GaN intermediate protection layer, inserted between the low-temperature-grown buffer layer and the high-temperature-grown GaN epilayer, was used for growing cubic GaN on GaAs (100) substrates by metalorganic vapor-phase epitaxy. The intermediate protection layer was grown at moderate temperatures to prevent GaAs substrate from thermal decomposition. This technique enables us to grow cubic GaN on GaAs substrates at higher growth temperatures. Even at the growth temperature of high as 980 degreesC, the interface between GaN layer and GaAs substrate is still smooth owing to the introduction of the intermediate protection layer. Photoluminescence and X-ray diffraction measurements showed that the crystal quality of the cubic GaN layer was improved by the realization of high-temperature growth using an intermediate protection layer.