Ultrathin La2O3 gate dielectric films were prepared on Si substrate using La(tmhd)(3) source by low pressure metalorganic chemical vapor deposition (MOCVD). The growth processing, interfacial structure and electrical properties have been investigated by various techniques. The ultrathin films deposited at 600 show amorphous structure with smaller roughness of similar to0.2 nm and larger band gap of E-g = 6.18 eV. This is attributed to the interfacial layer existence of compositionally graded La-Si-O silicate. Due to the chemical instability of La2O3 films in ambient, it can absorb vapor and carbon dioxide, which leads to the deterioration of electrical properties. By introducing Al2O3 capping layer, the reliable value of equivalent oxide thickness around 1.8 nm of La2O3/Si has been achieved. (C) 2004 Elsevier B.V. All rights reserved.