Though it is a long time since the combined cycle plant performance was in the spotlight for its high thermal efficiency, it is possible to achieve a better combined cycle performance using higher gas turbine temperatures. The next generation of large, heavy-duty, single-shaft gas turbine G series gas turbines with a turbine inlet temperature of 1 500°C has been developed by Mitsubishi Heavy Industries, Ltd. (MHI). Many advanced component technologies are employed in this turbine. The 501 G for 60 Hz utilities has been performing well at the combined cycle plant verification test at MHI since June, 1997. The 701 G 1s for 50 Hz utilities are being manufactured now and the first one was tested at the end of 1997 fiscal year. After that ,it will be installed at the "Higashi Niigata power plants No.4" of Tohoku Electric Power Co., Inc. and will begin trial operation in October, 1998. Commercial operation will be begun in July, 1999, and will be the first commercial 1 500°C class gas turbine combined cycle commercial plant in the world.