The MOS structure prepared on n-type Si substrate with SiO2/HfO2 gate dielectric layers was formed by 5 nm HfO2 oxide deposited by atomic layer deposition on 0.6 nm SiO2 oxide film prepared with nitric acid oxidation of Si (NAOS) in similar to 100% HNO3 vapor. The set of this MOS structure was annealed in N-2 atmosphere at 200, 300 and 400 degrees C for 10 min to stabilize the structure, to decrease the interface states density and leakage current density. The both acoustic deep level transient spectroscopy (A-DLTS) and acoustoelectric response signal versus gate voltage dependence (U-ac-U-g characteristics) were used to characterize the interface states and the role of annealing treatment, except ordinary electrical investigation represented by current-voltage and capacitance-voltage measurements. The main interface deep centers with activation energies similar to 0.30 eV typical for dangling-bond type defects were observed as well as a particular influence of annealing treatment on the interface states. The obtained results are analyzed and discussed. (C) 2012 Elsevier B. V. All rights reserved.