The electrical conduction mechanism in zirconium oxide (ZrO2) thin films as a function of temperature T and electric field E was studied. Al/ZrO2/p-Si metal-insulator-semiconductor capacitors were fabricated. With the Al electrode biased negative, the conduction mechanism in an electrical field of 0.81 < E < 1.40 MV/cm and in the temperature range of 375 < T < 450 K was modified Schottky emission. The intrinsic barrier height between Al and ZrO2 was 1.06 eV. At a higher electrical field of 1.50 < E < 2.25 MV/cm and higher temperatures of 375 < T < 450 K, the electrical conduction was dominated by modified Poole-Frenkel emission. The extracted trap level was 0.83 eV. With the Al electrode biased positive, the conduction mechanism was Schottky emission at the electrical field 0.20 < E < 0.60 MV/cm and higher temperatures of 425 < T < 450 K. The barrier height between Si and ZrO2 was 1.0 eV. Based on the above results, an energy band diagram of the Al/ZrO2 /p-Si system is proposed. (c) 2005 The Electrochemical Society. [DOI: 10. 1149/1.1855833] All rights reserved.