The kinetics for the replacement process of hydrogen by deuterium at the (100)Si/SiO2 interface is studied. Metal–oxide–semiconductor devices were initially annealed in hydrogen and then reannealed in deuterium at various temperatures for various durations. The deuterium concentration CD, defined as the percentage of interface defects passivated by deuterium, was then determined by a technique that is solely based on electrical measurements. From fundamental kinetics, activation energy E for replacing hydrogen by deuterium at the (100)Si/SiO2 interface is determined to be 1.84 eV. This result suggests that the replacement of hydrogen by deuterium involves a process of the dissociation of molecular deuterium at the interface. © 2001 American Institute of Physics.