Thermodynamic analysis was conducted to determine the conditions necessary for the selective epitaxial growth (SEG) of SiC on masked Si substrates, and these results were compared to blanket SiC epitaxy on plain Si. For blanket SiC epitaxy, the proper deposition conditions leading to single‐phase SiC without Si or graphite codeposition were determined. For SiC SEG, the additional constraint, that no significant mask etching should occur, was considered. All process parameters, i.e., temperature, pressure, C/Si, Cl/Si, and in the gas mixture significantly affect when epitaxy is possible, but the optimal deposition parameters change with the presence of a large amount of Si and/or (from the solid phases). The inclusion of the substrate and mask in the computation is more complete and accurate than only considering the gas sources in predicting practical deposition conditions. Adding Cl or providing more carbon than silicon in the gas sources (e.g., increasing C/Si ratio to 4) helps to suppress Si codeposition. No graphite codeposition takes place under any of the parameter ranges considered.