Dynamic temperature configuration and current filamentation in single‐crystal silicon films on sapphire substrates were studied with high‐amplitude constant‐current pulse excitation using Sunshine's stroboscopic technique. Temperature configurations vary greatly depending upon the pulse duration and amplitude, electrode geometry magnitude of heat flow into the substrate, and magnitude of transverse heat flow. Filamentation occurs in two steps, each accompanied by a voltage drop. An initial broad filament forms as local regions rise in temperature beyond the peak of the resistivity‐temperature curve of the silicon. The second filamentation is a narrow melt channel that forms interior to the initial filament. A time‐dependent computer simulation is presented that includes both the heat flow into the substrate and transverse heat conduction. The model shows that a stable‐current filament can exist without a melt transition, but only for a very restricted range of current levels.