Abstract We have found that at the metal-electrolyte interface an Au(100)−(1×1) surface can reconstruct already at room temperature into its hexagonal (5×20) form, when a negative potential is applied. The activation barrier for reconstruction is obviously lowered significantly by charging the electrode negatively, which can be rationalized within the model of Heine and Marks by the accumulation of excess electrons at the surface. The transition (1×1)→(5×20) depends strongly on the electrode potential and, to some extent, on the electrolyte composition. In 5 mM H 2SO 4 at −0.4 V versus SCE, the Au(100)−(1×1) surface can reconstruct almost completely into (5×20) within a few minutes. The kinetics of this potential-induced surface reconstruction has been investigated and its mechanism will be briefly discussed.