A thermal model for the initiation of programming in metal-to-metal amorphous-silicon antifuses is described. The current and field crowding at the edges of the via cause the temperature at the via corners to increase due to Joule heating. Programming is initiated when the temperature at the via edges reaches the melting temperature of amorphous silicon. The model presented in this work explains how the thickness of the amorphous-silicon layer, the ambient temperature, and the duration of the programming pulse affect the programming process.