Selectivity control in silicon selective epitaxial growth (SEG) for deep contact patterns, which is one of the key processes for silicon-based stacked devices and cell switches for next generation memories, was studied. Absolute values of selectivity loss during silicon SEG using the most popular H 2/dichlorosilane (DCS)/HCl gas system were evaluated using a commercialized inspection tool in 200mm wafers with real contact patterns. It was revealed that HCl=(DCS + HCl) ratio and the contact structure played a crucial role in suppressing selectivity loss. The number of selectivity losses in an entire wafer was less than 100 when the HCl=(DCS + HCl) ratio was larger than 0.41. The vertical pn diode prepared using the silicon SEG process with elaborate selectivity control showed more remarkable electrical abilities to accommodate current flow than polycrystalline silicon (poly-Si), including the ideality factor and swing, and reverse leakage current.