A new cyclopropanation reaction involving C alpha-Si bond insertion of alkylidene carbenes derived from alpha-silyl ketones has been developed. This unprecedented alkylidene carbene reactivity features excellent selectivity for insertion into C alpha-Si bonds rather than insertion into C gamma-H bonds or addition to gamma,delta-double or -triple bonds. The selectivity trend clearly indicates that the alpha-oxygen in the tether significantly promotes C gamma-H insertion, although the C alpha-Si bond insertion still competes effectively.