We have investigated a sputter-deposited Al2O3/HfO2 stack as a blocking layer of metal–oxide–nitride–oxide–silicon capacitors. Compared with a SiO2 blocking layer, the sample with Al2O3/HfO2 stack shows lower write/erase (W/E) voltage, higher speed, and longer data retention time. The improvement of electrical characteristics can be explained by lower leakage current density and less voltage drop of high-k blocking layer which in turn increase the effective thickness of tunneling oxide. After stressing the W/E voltage of ±10 V voltage for 1 ms, the flat-band voltage shift of 4 V and 10 years of retention time was obtained.