A manufacturing method of a semiconductor device capable of efficiently inspecting whether a metal silicide layer is sufficiently formed is provided. The manufacturing method is provided with the steps of forming a metal layer over a semiconductor layer containing silicon; forming a metal silicide layer over a surface of the semiconductor layer by heating the semiconductor layer and the metal layer; generating image data by performing color imaging of the metal silicide layer from above the metal silicide layer; calculating saturation of the metal silicide layer by processing the image data; and judging the formation amount of the metal silicide layer on the basis of the calculated saturation.