The high-temperature dielectric properties of thin-film aluminum nitride (AIN) that was pulsed-laser deposited (PLD) on heavily doped n-type 6H and 4H-SiC substrates are investigated from 25 to 450 degreesC. Identical, very low leakage current densities (< 1 x 10(-2) A/cm(2) at 450 C for a 2-MV/cm electric field) are reported for both polytypes. The primary high-temperature leakage mechanism appears to be Schottky emission with zero-field barrier heights for 6H and 4H of 1.68 and 1.55 eV, respectively.