High-entropy ceramics exhibit novel intrinsic properties. Hence, they have been explored for a wide range of applications ranging from thermal insulation and energy storage to advanced optical components. Recently, the semiconductor industry has faced a demand for higher-performance chips, necessitating higher aspect ratios in wafer fabrication and further miniaturization of linewidths. Therefore, novel materials with high plasma etching resistance and minimal contaminant generation are needed. The plasma-etching resistance displayed by high-entropy ceramics can be an innovative solution to this emerging challenge. In this study, we successfully fabricated single-phase high-entropy sesquioxide ceramics with high optical transparency, dense microstructure, and minimal residual pores. A structural analysis of the fabricated samples revealed a single-phase structure with excellent phase homogeneity. An evaluation of the plasma-etching resistance of high-entropy ceramics revealed for the first time a low etching rate of 8 nm/h compared with that of conventional plasma-resistant materials. These comprehensive characterizations of high-entropy ceramics indicate that they are promising candidates for significantly improving the production yield of semiconductors and for a wide range of potential applications, such as next-generation active optical ceramics.