The present invention provides a method for analyzing a silicon substrate, by which impurities such as a very small amount of metal in a silicon substrate provided with a thick nitride film can be analyzed with high accuracy with ICP-MS, and is characterized by use of a silicon substrate analysis apparatus including an analysis scan port having a load port, a substrate conveyance robot, an aligner, a drying chamber, a vapor phase decomposition chamber, an analysis stage and a nozzle for analysis of a substrate; an analysis liquid collection unit; and an analyzer for performing inductive coupling plasma analysis.