The substitution of the SiO2 gate oxide in MOS devices by a material with a high-k dielectric constant is being deeply studied nowadays to solve the problem of the leakage currents that appear with the progressive scaling of SiO2 thickness. To improve the quality of the high-k/Si interface a very thin SiO2 film is grown between both materials. In this work, HfO2/SiO2 stacks with different SiO2 thickness were subjected to different types of stress (static and dynamic) to analyze the effect of this interfacial layer of SiO2 in the degradation of the stack. The results show that the dielectric degradation depends on the stress applied and that the thickness of the SiO2 interfacial layer influences the advanced stages of the stack degradation. © 2007.