By using the Ni-Ta alloys fabricated by interdiffusing stacks of Ni and Ta, we have experimentally investigated the work function (φm) controllability and thermal stability required for the advanced metal gate MOSFETs. The capacitancevoltage (C-V) measurement of the interdiffused Ni/Ta and Ta/Ni stacks revealed that the φm of the Ni-Ta alloy was changed from that of pure Ni and Ta samples. The φm uniformity of the intediffused Ni-Ta alloy was found to be comparable to that of the pure Ni by observing the microscopic φm by scanning Maxwell-stress microscopy. The excellent thermal stability of the interdiffused Ta/Ni stack was revealed up to 900°C. From these experimental results, the Ni-Ta alloy is promising candidate for the metal-gate MOSFETs.