MOS capacitors were fabricated to study electrical and chemical properties of Ta-Mo metal alloy with ZrO₂. The work function of Ta-Mo alloy were varied from 4.1eV to 5.1eV by controlling the composition. When the atomic composition of Mo is 10%, good thermal stability up to 800℃ was observed and work function of MOS capacitor was 4.1eV, compatible for NMOS application. But pure Ta exhibited very poor thermal stability. After 600℃ annealing, equivalent oxide thickness of tantalum gate MOS capacitor was continuously decreased. Barrier heights of Ta-Mo alloy and pure metal that supported the work function values were calculated from Fowler-Nordheim analysis. As a result of these electrical experiments, Ta-Mo metal alloy with ZrO₂ is excellent gate electrode for NMOS.