Alternating cyclic, A.C., selective area epitaxial growth of silicon in the Si-H-Cl and Si-H-Cl-Ar systems was carried out in a hot wall, low pressure epitaxial reactor, using patterned thermal oxide masks. The A.C. process is based on the existence of an embedded disproportionation reaction within the overall deposition chemistry, which provides an effective mechanism for preventing the formation of nuclei in the areas where deposition is not desired. This disproportionation chemistry is made dominant cyclically, by pulsing the hydrogen off and on periodically, in order to eliminate incipient nucleation. Experiments were conducted over a portion of the available parameter space, as determined by extensive thermodynamic analyses, using a reference non-A.C. deposition process as a control, and comparing it with different A.C. frequencies. Thus, the temperature was varied from 750 to 1000 degrees C, the pressure from 1.5 to 10 Torr, the H-2/SiCl4 ratio from 12.5/1 to 100/1, the Ar/H-2 ratio from 0 to 11. Total system now rate was varied from 2.04 slpm to 24.04 slpm, with the argon flow rate accounting for 0 to 22 slpm of these total values. Oxide coverage was varied from 100% (worst case situation) to 0% (best case situation). Epitaxial thickness varied between 0.1 and 3.5 mu m. It was found that the substrate topology, and various experimental conditions influenced, to varying degrees, the tendency for spurious nucleation in the masked areas. However, under all conditions, the A.C. technique prevented formation of spurious nuclei, guaranteeing essentially 100% selectivity control.