In this study, the effect of microwave annealing (MWA), which has been attracting considerable attention as a low-thermal-budget method, on the high-k materials required for next-generation ultrahigh-integration semiconductor devices is investigated. Metal-oxide-semiconductor (MOS) capacitor-structure devices are fabricated using HfO₂ films, which are typical high-k materials; post deposition annealing (PDA) is then performed by MWA and compared to conventional thermal annealing (CTA). The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the fabricated HfO₂ MOS capacitors are measured to evaluate the leakage current, time-zero dielectric breakdown (TZDB), time-dependent dielectric breakdown (TDDB), and frequency dispersion. Compared to the as-deposited state, the PDA-treated HfO₂ dielectric film is found to have reduced trap density, improved dielectric breakdown, frequency dispersion, and lifetime. In particular, the high-k HfO₂ thin films treated with MWA exhibit excellent surface properties, including a low root-mean square roughness (Rq) of 0.141 nm, thickness of 49.3 nm, and low inter face trap density (Dit) of 7.82 × 1012 cm-2eV-1 and electrical properties such as a high breakdown electric field (EBD) of 10 MV/cm, and high breakdown to charge (QBD) of 1,000 C/cm². As a result, the MWA-treated high-k HfO₂ thin films are smoother and denser than the CTA-treated thin films, and show better electrical properties and reliability, suggesting that the defects at Si the interface as well as in the high-k films are effectively removed.