The selective area chemical vapor deposition of silicon using the alternating cyclic, A. C., hydrogen reduction of SiCl4 is discussed from the perspective of a thermodynamic analysis over a broad pressure and temperature range. The analyses incorporated the thermodynamic data for all the known species in the Si-H-Cl and Si-H-Cl-Ar systems. The A. C. concept is based on the sequential hydrogen reduction of SiCl4, followed cyclically by the etching of spurious nuclei of silicon via an embedded disproportionation reaction. The analysis indicates the feasibility of the A. C. technique and identifies the temperature and total system pressure range for maximum process efficiency. The effect of small errors in the thermodynamic data of the vapor phase species SiH2Cl2 on the results of the calculations has also been investigated.