Tantalum pentoxide (Ta2O5) thin film with an initial thickness of 10.5 urn was deposited onto p-type silicon substrate by chemical. vapor deposition (CVD), and subsequently annealed in O-2 ambience at 500 to 800 degreesC for 30 min. It was found that with proper thermal treatment, we could reduce the leakage current down to 6.4 x 10(-8) A cm(-2) at 3 V, although, the effective oxide thickness will also increase from 2.42 to 3.50 nm. Higher annealing temperatures will result in a rougher sample surface and higher leakage current due to Ta2O5 crystallization. Before the crystallization of the Ta2O5 film, the leakage current was dominated by the Poole-Frenkel emission mechanism. For the crystalline Ta2O5 film, the conduction mechanism at low electric field was not obvious and could be affected by the formation of the grain boundary in the Ta2O5 film. (C) 2002 Elsevier Science B.V. All rights reserved.