Germanium-tellurides (GeTe) are promising thermoelectric materials owing to their outstanding thermoelectric (TE) performance in the mid-temperature range. Meanwhile, the temperature-dependent structural transition in GeTe-based alloy could directly affect the gradient of the transport properties. Microstructural engineering, as well as stoichiometric controlling, are powerful approaches to suppress the phase transition. Examples can be given in Cu2S-GeTe alloy, which appears 149% reduction in thermal conductivity. In addition, the transition temperature shifts toward higher temperature in order to enlarge the temperature range of -GeTe. In short, stoichiometric controlled Cu2S-GeTe shows superior TE performance through microstructural engineering.