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Sputter deposited alumina thin films were investigated with regard to their performance as high-temperature electrical insulators. A target application of such dielectric films is in metal pressure sensor cells intended for high-temperature operation. The leakage behavior of sputtered alumina films was investigated by analyzing the temperature-dependence of the I-V characteristics of alumina films deposited on silicon and Haynes 230 substrates. Silicon substrates were used to analyze the leakage behavior under optimally controlled substrate conditions. Haynes 230, a nickel-based superalloy, was used as a substrate material to simulate conditions expected in a high-temperature metal pressure cell. In order to compare the dielectric performance under conditions of closely similar substrate quality, the topography of the Haynes 230 substrates was improved by applying a lapping process. From our results, we derive an estimate of the maximum operating temperature of metal pressure sensor cells.