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. ©1995 American Institute of Physics.