High-temperature treatment of the melt (HTTM) is a very simple and available technique for stabilizing and improving the service properties of parts. It consists in heating the melt to a certain critical temperature, a hold, and cooling. The present paper is devoted to the effect of HTTM, the standard heat treatment, and long isothermal holds at the service temperatures on the structure and properties of castable high-temperature nickel alloy ZhS6U.