HfO2 gate dielectric films with a blocking layer of Al2O3 inserted between HfO2 layer and Si layer (HfO2/Si) were treated with rapid thermal annealing process at 700 ℃. The interfacial structure and electrical properties were reported. The results of X-ray photoelectron spectroscopy showed that the interfacial layer of SiOx transformed into SiO2 after the annealing treatment, and Hf-silicates and Hf-silicides were not detected. The results of high-resolution transmission electron microscopy indicated that the interfacial layer was composed of SiO2 for the annealed film with blocking layer. The results of the electrical measurements indicated that the equivalent oxide thickness decreased to 2.5 nm and the fixed charge density decreased to –4.5×1011/cm2 in comparison with the same thickness of HfO2 films without the blocking layer. Al2O3 layer could effectively prevent the diffusion of Si into HfO2 film and improve the interfacial and electrical performance of HfO2 film