The relationship between blistering, H content and de-passivation of the dangling bonds has been studied in annealed hydrogenated a-Si/a-Ge superlattice (SL) nanostructures grown by RF sputtering. Measurements have been carried out by ERDA, IR absorbance and AFM. By comparison with parallel investigations on a-Si and a-Ge single layers it has been established that the bubbles causing blistering in the annealed SLs very likely start to grow in the Ge layers of the SL because H is released from Ge much earlier than from Si. It is shown that the H forming the bubbles is only a fraction of the H liberated during the annealing. (C) 2012 Elsevier B. V. All rights reserved.