A plasma etching apparatus for a semiconductor wafer generates plasma in a plasma generation space between a susceptor and a showerhead. A shield member is detachably disposed inside the sidewall of a process chamber to prevent reaction products from sticking to the sidewall. A window device is arranged to lead plasma light emitted from plasma out of the process chamber. The window device includes a quartz window plate airtightly attached to the sidewall of the process chamber. The window device also includes an aluminum light guide having a number of capillary through holes for guiding the plasma light to the window plate, and a sapphire cover plate disposed between the window plate and the light guide and covering the openings of the through holes. The light guide and the cover plate are attached to the shield member.