Abstract: An etching system including a chamber, lower and upper electrodes provided in the chamber, a plasma light monitoring window provided in a side wall of the chamber, and an endpoint detecting device mounted outside the plasma light monitoring window. The plasma light monitoring window may be formed of high-purity aluminum oxide (Al.sub.2 O.sub.3) as a transparent ceramic, so that plasma light generated in the chamber can be efficiently transmitted through the plasma light monitoring window to the endpoint detecting device. Accordingly, even when the plasma light monitoring window is etched, its transparency is not lost. Furthermore, since the content of impurity in the window is low, contamination of an object to be etched with the impurity can be suppressed.