We contribute with this paper to the understanding of positive charge build up upon hole injection in SiO2 known to be an important degradation process. Our results are in agreement with a recently proposed model of charge generation [4,6]. We have observed the release of HD molecules upon hole injection in MOS capacitors that received a post-metallisation annealing in 100 kPa D-2 at 680 K. We provide evidence that the release of every HD molecule is related to the capture of one hole by one O(3)equivalent toSi-D centre. This centre is converted into the neutral O(3)equivalent toSi centre accompanied by the liberation of one deuteron D+, which, when neutralised, recombines with H giving the observed HD and when trapped, is responsible for the positive charge build up. The release of HD is suppressed when the number of generated O(3)equivalent toSi centres is high enough to trap all the generated HD. This occurred when only 25% of the initial O(3)equivalent toSi-D groups had dissociated by hole trapping. The positive charge build up was found to be dependent on the sample treatment indicating the strong influence of external sources of hydrogen in the described processes. The O(3)equivalent toSi groups generated upon hole injection were found to be located close to the surface, distributed over a layer with a thickness dependent on strength of the electric field applied during the hole injection, i.e. 220 nm for 1.0 MV/cm and 400 nm for 2.0 MV/cm. (C) 2002 Elsevier Science Ltd. All rights reserved.