As the gate oxide thickness decreases below 2 nm, the gate leakage current increases dramatically due to direct t tunneling current. This large gate leakage current will be an obstacle to reducing gate oxide thickness for the high speed operation of future devices. A MOS transistor with Ta2O5 gate dielectric is fabricated and characterized as a possible replacement for MOS transistors with ultra-thin gate silicon dioxide. M Mobility, Id-Vd Id-Vg, gate leakage current, and capacitance-voltage (C-V) characteristics of Ta2O5 transistors are evaluated and compared with SiO2 transistors. The gate leakage current is three to five orders smaller for Ta2O5 transistors than SiO2 transistors.