We fabricated metal-oxide-semiconductor (MOS) devices with Pt/Ta2O5 gate stacks and investigated their electrical and structural properties. As increasing RF magnetron sputter-deposition time of Ta2O5 film, the values of equivalent oxide thickness (EOT) and flat band voltage (VFB) increase whilst the density of interfacial trap (Dit) gradually decreases. The effective metal work function (Φm,eff) of Pt metal gate, extracted from the relations of EOT versus VFB are calculated to be ∼5.29 eV, implying that Fermi-level pinning in Ta2O5 gate dielectric is insignificant.