The thermoelectric performance and thermal stability of high-entropy sulfides (Cu7Mg2Sn2ZnGeS13, Cu5MgSnZnSiS9, and Cu7Mg2Sn2ZnSiS13) were studied and compared with copper-based monosulfides (Cu2S) and binary sulfides (Cu12Sb4S13). High-entropy sulfides exhibit superior thermal stability, characterized by higher decomposition onset temperatures and minimal weight loss, maintaining their structural stability up to 750 ℃. Cu7Mg2Sn2ZnSiS13 demonstrates a peak ZT of 0.52 at 500 ℃. Further optimization through sulfur compensation (Cu7Mg2Sn2ZnSiS13.5) results in a 200 % improvement of the peak ZT value to 1.12 at 550 ℃, which is comparable to other pristine copper-based sulfides, while being more eco-friendly and cost-effective. Entropy engineering provides a new way to improve the inherent thermal and structural stability of sulfides and can also optimize their thermoelectric performance using non-toxic and earth abundant cation elements.