<p>This study investigated the oxidation behavior of the MoNbTaTiV refractory high-entropy alloy after the application of a silicon pack cementation process, over the temperature range of 600 °C–1300&#xa0;°C. The as-cast alloy exhibited a single BCC structure. Under high-temperature conditions, however, it experienced severe mass loss and surface degradation due to the formation of volatile oxides such as MoO₃ and V₂O₅, as well as non-protective oxides including Nb₂O₅ and Ta₂O₅. In the lower temperature range, localized disintegration of the metallic substrate was also observed, attributed to pesting phenomena. In contrast, the specimens coated with silicides demonstrated significantly improved oxidation resistance. The coating consisted of XSi₂/X₅Si₃ (X = Mo, Nb, Ta, Ti, V) and exhibited excellent oxidation resistance across the entire temperature range tested. The refractory high-entropy silicide layer effectively protected the substrate at both low and high temperatures. In particular, at elevated temperatures, the formation of a continuous SiO₂ protective layer effectively suppressed oxygen diffusion, thereby inhibiting oxide scale growth and crack formation. The oxidation behavior of the MoNbTaTiV alloy and its Si-coated alloy is discussed in relation to the corresponding microstructure and phase.</p> Graphical Abstract <p></p>