A structural study of a fabricated GaN/AlN/SiC/Si structure is reported. The GaN layer is grown by molecular beam epitaxy (MBE) on carbonized Si substrates where SiC is covered by a thin AlN buffer layer before GaN deposition. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) studies allow evaluating the structural quality of the obtained SiC and GaN. As a first step, Si carbonization in a rapid thermal chemical vapor deposition reactor (RTCVD) is used to obtain ultra-thin beta-SiC(111)//Si(l 11) structures where SiC exhibits good crystalline orientation, homogeneity and structural quality. The latter allows to obtain a thin SiC buffer between the Si substrate and the GaN layers. The grown GaN layer is thicker than one micron and results of electron diffraction indicate that the GaN layer is well aligned with the Si(I I I) substrate. The measured surface dislocation density is in the range of 10(9) cm(-2), thus SiC/Si templates improve the GaN structural quality compared to pure silicon substrates.