An improved antifuse uses metal penetration of either a P-N diode junction or a Schottky diode. The P-N junction, or Schottky diode, is contacted by a diffusion barrier such as TiN, W, Ti-W alloy, or layers of Ti and Cr, with a metal such as Al. Al-CU alloy, Cu, Au, or Ag on top of the diffusion barrier. When this junction is stressed with voltage pulse producing a high current density, severe joule heating occurs resulting in metal penetration of the diffusion barrier and the junction. The voltage drop across the junction decreases by about a factor of ten after the current stress and is stable thereafter. Alternatively, a shallow P-N junction in a silicon substrate is contacted by a layer of metal that forms a silicide, such as Ti, Cr, W, Mo, or Ta. Stressing the junction with a voltage pulse to produce a high current density results in the metal penetrating the junction and reacting with the substrate to form a silicide.