Results are presented for the thermal oxidation behavior of four types of sputtered tantalum films between 100° and 525°C. These films are bcc tantalum, &bgr;‐tantalum, a porous &bgr;‐tantalum, and tantalum nitride (Ta2N). All four types of films show parabolic oxidation kinetics and the formation of adherent Ta2O5(tantalum oxy‐nitride for Ta2N films) with bright interference colors. The first three types of films dissolve about 12 at.% oxygen, which is much higher than the oxygen solubility found in bulk tantalum, and the films show a different degree of suboxide formation than bulk tantalum. The activation energies for oxygen diffusion in the metal and for oxide growth are 1.2 and 1.4 eV, respectively. The dielectric properties of the thermal oxide are discussed in terms of the defects in the oxide.