Tantalum pentoxide (Ta2O5) films have been deposited using an Atomic Layer Deposition (ALD) process based on the reaction of pentakis dimethyl amido tantalum (PDMAT) and H2O at 250°C. Films were deposited on native oxide Si(100) surfaces and native oxide and etched GaAs(100) surfaces. Linear growth at ~0.6 Å/cycle has been confirmed using spectroscopic ellipsometry. Atomic Force Microscopy indicates that the films are smooth and x-ray diffraction data indicate that the as-deposited films are amorphous, and begin to crystallize after anneals at 800°C (3 min, Ar). These observations are mirrored in the infrared spectra. Film composition has been studied using x-ray photoelectron spectroscopy (XPS) and it has been found that the films are slightly over oxidized. The interface of films deposited on native oxide and etched GaAs surfaces has also been studied using XPS and high resolution transmission electron microscopy. Data from both techniques indicate that an interface cleaning mechanism similar to that observed for other amide based ALD processes may be present.