In this Letter, the robust ferroelectric properties of low-temperature (350 °C) Hf0.5Zr0.5O2 (HZO) films are investigated. We demonstrate that the lower crystallization temperature of HZO films originates from a densified film deposition with an anhydrous H2O2 oxidant in the atomic layer deposition process. As a consequence of this densification, H2O2-based HZO films showed completely crystallinity with fewer defects at a lower annealing temperature of 350 °C. This reduction in the crystallization temperature additionally suppresses the oxidation of TiN electrodes, thereby improving device reliability. The low-temperature crystallization process produces an H2O2-based HZO capacitor with a high remanent polarization ( Pr), reduced leakage current, high breakdown voltage, and better endurance. Furthermore, while an O3-based HZO capacitor requires wake-up cycling to achieve stable Pr, the H2O2-based HZO capacitor demonstrates a significantly reduced wake-up nature. Anhydrous H2O2 oxidant enables the fabrication of a more reliable ferroelectric HZO device using a low process thermal budget (350 °C).