1. A method of inspecting a process for manufacturing a semiconductor device, used to determine the status of a processing operation during the manufacturing process, comprising: detecting an image of a desired area of a surface of a semiconductor workpiece after it has been subjected to the processing operation, by using an image signal detector; detecting image signal intensity at each pixel of a plurality of pixels of the image signal detector; and determining the status of the processing operation based on the relationship between the image signal intensity and the number of pixels at each of certain levels of the image signal intensity.