The formation of the potential barrier at the metal‐silicon contact has been investigated. Special emphasis has been given to the study of aging of gold–n‐type‐silicon Schottky diodes. The behavior of the electrical properties as a function of time of exposure to air has been studied, showing that the increase of the barrier height, from 0.5–0.6 eV up to the typical 0.8‐eV value is related to the diffusion of oxygen (or water vapor) from the ambient through the metal contact and its accumulation at the interface. In addition, preliminary results onp‐type silicon are reported. A phenomenological model based on the behavior of oxygen with respect to the metal involved is proposed to describe the aging for any metal deposited onn‐ orp‐type silicon.