According to the present invention, there is provided a semiconductor device fabrication method comprising: measuring light emission intensity of at least one type of wavelength contained in light emitted from a plasma, when one of nitriding, oxidation, and impurity doping is to be performed on a surface of a semiconductor substrate in a processing vessel by using the plasma; calculating, for each semiconductor substrate, an exposure time during which the semiconductor substrate is exposed to the plasma, on the basis of the measured light emission intensity; and exposing each semiconductor substrate to the plasma on the basis of the calculated exposure time, thereby performing one of the nitriding, oxidation, and impurity doping.