We have deposited AlN thin films, which are highly thermally conductive insulating films, at room temperature independent of substrate and ambient temperature. We also evaluated the practicality of the obtained AlN thin film by measuring its thermal conductivity in the thermoelectric material Bi2
using the 3ω method. AlN thin films were deposited on Bi2
thin films, Ni thin plates and Cu thin plates using pressure gradient sputtering. As a result, an optimum insulating film with a thickness of about 800 nm was obtained after 2 h of deposition at a distance of 10 cm between the target and the sample. The thermal conductivity of Bi2
was obtained to be 0.56±0.05 W/(m･K) by using the AlN thin film in the thermal conductivity measurement by the 3ω method. The thermal conductivity of Bi2
measured using polyimide, which was conventionally used in the 3ω method, was 0.52±0.25 W/(m･K), which means that the measurement error was successfully reduced significantly. The above results indicate that this film is useful as a highly thermally conductive insulating thin film.