The epitaxial wafer is expected to become the main substrate of semiconductor devices for super large diameter wafers over 300 mm. We are developing the 400 mm epitaxial wafer under the super silicon project. Our first technical accomplishment was the development of a low temperature SiH4 gas epitaxial growth process, followed by the manufacture of a single wafer spin cleaner and original epitaxial furnace for 400 mm diam wafers. We were successful in growing the entire surface of a 400 mm diam wafer by a series of processes that were conducted using these developments.