We report the observation of all-optical switching in a metal–semiconductor–metal waveguide structure. A silicon-on-insulator waveguide with aluminum interdigitated fingers deposited on the surface and overcoated with amorphous silicon provided high-efficiency coupling and switching of Nd:YAG laser pulses. This structure is fully compatible with very large scale integrated manufacturing processes and represents a substantial leap forward in the quest for full-scale integration of silicon-based optoelectronic systems.