The authors describe the large-area synthesis of WSe₂ monolayers using a gas-phase reaction of WO₃ and Se powders in a hot-wall CVD chamber. The reaction was conducted at temperatures ranging from 750°C to 925°C, with the hydrogen gas playing a crucial role in activating the reaction. At 850°C, triangular and single-crystalline WSe₂ monolayer flakes were grown, while at 750°C, a continuous and polycrystalline monolayer film was formed. Raman and photoluminescence (PL) spectra confirmed the monolayer and bilayer structures, with characteristic peaks at 248 cm⁻¹ and 259 cm⁻¹ for monolayer WSe₂, and a strong emission at ~760 nm for monolayer WSe₂. High-resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) patterns further confirmed the hexagonal lattice structure of the monolayers. The study highlights the importance of temperature and gas conditions in controlling the morphology and crystallinity of WSe₂ monolayers.The authors describe the large-area synthesis of WSe₂ monolayers using a gas-phase reaction of WO₃ and Se powders in a hot-wall CVD chamber. The reaction was conducted at temperatures ranging from 750°C to 925°C, with the hydrogen gas playing a crucial role in activating the reaction. At 850°C, triangular and single-crystalline WSe₂ monolayer flakes were grown, while at 750°C, a continuous and polycrystalline monolayer film was formed. Raman and photoluminescence (PL) spectra confirmed the monolayer and bilayer structures, with characteristic peaks at 248 cm⁻¹ and 259 cm⁻¹ for monolayer WSe₂, and a strong emission at ~760 nm for monolayer WSe₂. High-resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) patterns further confirmed the hexagonal lattice structure of the monolayers. The study highlights the importance of temperature and gas conditions in controlling the morphology and crystallinity of WSe₂ monolayers.