Since thin films of tantalum compounds are of interest in integrated circuit technology, the preparation and properties of TaON and Ta//3N//5 were investigated. TaON was found to be nonstoichiometric and to be stable over a wide range of gas compositions. TaON is also a semiconductor; its electric conductivity varies by 3 1/2 orders of magnitude as the nitrogen and oxygen contents are varied. Ta//3N//5 has a somewhat lower electric conductivity, and it does not seem to be nonstoichiometric. The free energies of formation of both TaON and Ta//3N//5 at 1100 K were computed from the experimental results.