For the development of advanced LSIs, ultra-thin high-k gate dielectrics with a direct interface between a high-k film and a Si substrate will be necessary to achieve equivalent oxide thickness (EOT) of 0.5 nm or less. LaAlO₃ that has both a high dielectric constant of 25 and good interfacial thermal stability with Si, has been considered to have a high potential for realizing such a small EOT value. In this study, a LaAlO₃ gate dielectric with both ultra-thin EOT and low leakage current was successfully fabricated by optimizing the deposition process of the dielectric. We found that the deposition of LaAlO₃ at high temperature is quite important for the excellent characteristics of LaAlO₃ gate dielectric.