Empirical information about surface flashover of silicon in a vacuum ambient which shows that in breakdown the current is carried primarily inside the semiconductor is presented. This observation shows that the physical processes responsible for flashover of silicon are fundamentally different from those assumed in the standard model for flashover of insulators. When breakdown occurs, visible emission from a plasma in the ambient just outside the silicon surface is observed. This plasma may influence the course of the breakdown, but it does not appear to be the cause of the breakdown event. >