Several high nickel content super alloys are commonly used as materials of construction for supercritical water reactors due to their oxidative resistance and mechanical properties. Two common alloys are Hastelloy C276 and Inconel 625 and have been used in multiple research projects involving supercritical water and supercritical water oxidation at 650°C at 5000 psig and 710°C at 3500 psig. Both yield strength and tensile strength of Hastelloy C276 and Inconel 625 are relatively constant over a broad range of temperatures, but rapidly drop off at higher temperatures and are not suitable as a material for supercritical water reactors whose local temperature is expected to exceed 800°C. Haynes Alloy 230 is an alloy designed for high temperature and high pressure applications in oxidative environments. It has substantially higher yield and tensile strength than Hastelloy C276 and Inconel 625 at 800°C making it a suitable material of construction for high temperature supercritical water reactors. A tubular 1” inner diameter Haynes Alloy 230 reactor was designed and developed for supercritical water applications up to 800°C at 5250 psig. This paper discusses the performance of Haynes Alloy 230 as reactor construction alloy in comparison to Hastelloy C276 and Inconel 625 for supercritical water applications. In particular, the Haynes 230 alloy reactor was used for supercritical water reformation process study which requires the reaction temperature to exceed 800 ºC at high pressures. The laboratory demonstration validates the safety and suitability of Haynes 230 alloy as reactor construction material for high-temperature supercritical water reactors.