Effect of high temperature annealing in the temperature range of 600–900 °C on the electrical properties and microstructure of tantalum pentoxide (Ta2O5) thin film deposited by plasma‐enhanced chemical vapor deposition (PECVD) was studied. Leakage characteristics of the Ta2O5 thin film annealed at 600 °C were found to be the best in this study. However, it was observed that the leakage current in the polycrystalline Ta2O5 thin film decreased with increasing the annealing temperature above 800 °C after a peak for 700 °C annealing. The dielectric constant of the annealed Ta2O5 thin film was 26 after annealing at 600 °C, and decreased with the same tendency as the leakage current characteristics. Transmission electron microscopy (TEM) and x‐ray diffraction (XRD) analysis indicated that the microstructure of the Ta2O5 thin film annealed above 800 °C was of δ‐Ta2O5 with hexagonal crystal structure. Furthermore, TEM and AES observations revealed that Ta–O–Si transition layers were formed between the annealed Ta2O5 thin film and Si substrate. The electrical properties of the Ta2O5 films are discussed in terms of interface modification and film densification due to rapid thermal annealing treatment. © 1995 American Institute of Physics.