This invention provides an ignition system for a spark initiated internal combustion engine such as an Otto cycle engine. High voltage pulses are generated, for instance by way of an ignition coil, and these are passed to the respective spark gaps by way of semiconductor switches. These semiconductor switches are preferably bulk photoconductive switch devices which each comprise a light source and a photosensitive switch. These devices are under the control of control circuitry which activates and deactivates the light sources approximately to distribute the high voltage pulses to the spark plugs. These switches may be used to improve the rise time of the potential across the spark gap or to generate a plurality of sparks in one gap from a single pulse.