Rare-earth phosphates (REPO₄) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiC_f/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO–MgO–Al₂O₃–SiO₂ (CMAS). Nevertheless, a relatively high thermal conductivity (κ) of the REPO₄ becomes the bottleneck for their practical applications. In this work, novel xenotime-type high-entropy (Dy_1/7Ho_1/7Er_1/7Tm_1/7Yb_1/7Lu_1/7Y_1/7)PO₄ (HE (7RE_1/7)PO₄) has been designed and synthesized for the first time to solve this issue. HE (7RE_1/7)PO₄ with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 ℃ and good chemical compatibility with SiO₂ up to 1400 ℃. In addition, the thermal expansion coefficient (TEC) of HE (7RE_1/7)PO₄ (5.96×10⁻⁶ ℃⁻¹ from room temperature (RT) to 900 ℃) is close to that of the SiC-CMCs. What is more, the thermal conductivities of HE (7RE_1/7)PO₄ (from 4.38 W·m⁻¹·K⁻¹ at 100 ℃ to 2.25 W·m⁻¹·K⁻¹ at 1300 ℃) are significantly decreased compared to those of single-component REPO₄ with the minimum value ranging from 9.90 to 4.76 W·m⁻¹·K⁻¹. These results suggest that HE (7RE_1/7)PO₄ has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.