The buffer layers used in this study included an AlN/3C-SiC composite film stack and a single AIN layer. 3C-SiC in the composite film stack prepared by the two-step process functioned better as a buffer layer than that prepared by direct epitaxial growth. The composite buffer prepared by this method was compared with the single AIN buffer. The GaN films grown on the composite buffer were significantly less susceptible to film cracking than those grown on a single AIN buffer. Photoluminescence evaluation showed that the GaN films deposited on the composite buffer were narrower in full width at half maximum than those deposited on a single buffer. However, the GaN and AlGaN films grown on top of the single AIN buffer showed smoother top surface and resulted in higher electron mobility in the AlGaN/GaN heterojunction. Surface and film qualities of the GaN films grown on the composite buffer were improved by insertion of an AlGaN/GaN superlattice.