The effect of postdeposition oxidation of SiOx/ZrO2 gate dielectric stacks at different temperatures (500-700 degrees C) on the density of fixed charge and interface states is investigated. It is shown that with increasing oxidation temperature the density of negative fixed charge is reduced, but the density of interface states increases. The net positive charge observed after oxidation at T > 500 degrees C resembles the charge generated at the Si/SiO2 interface by hydrogen in the same temperatures range. This association is supported by the resistance of both types of charge against molecular hydrogen anneal but their fast removal in the presence of atomic hydrogen at 400 degrees C. Therefore, we propose that the observed oxidation-induced positive charge in the SiOx/ZrO2 gate stack may be related to overcoordinated oxygen centers induced by hydrogen. (C) 2000 American Institute of Physics. [S0003-6951(00)01338-3].