Rare earth oxides, such as La2O3 and Yb2O3, deposited on Si(100) were investigated for high-k gate insulator applications. La2O3 has the largest bandgap and smallest lattice energy among the rare earth oxides, while Yb2O3 has a smaller bandgap and larger lattice energy compared to La2O3. La2O3 showed excellent electrical properties, such as small capacitance equivalent thickness and low leakage current density with smooth film surface and interface after rapid thermal annealing (RTA) at 400-600degreesC. On the other hand, the surface of Yb2O3 thin film was easily roughened after RTA even at 400degreesC, and the leakage current density was higher compared to La2O3. The difference in characteristics for the films was considered to be attributed to the difference of their properties, such as bandgap and lattice energy. La2O3 was able to keep the amorphous phase at least up to 600degreesC RTA, and this seems promising for future high-k gate insulator applications. (C) 2003 The Electrochemical Society.