The aim of this study is to detect small amounts of impurities and defects affecting metal-oxide-semiconductor (MOS) device characteristics in SiO₂/Si samples, which is necessary for making electron spectroscopy for chemical analysis (ESCA) useful for device application. The process is not easy because X-ray-induced charging makes it difficult to determine chemical states accurately and also because the amount of impurities and defects is usually below the ESCA detection limit. We have found ways to make the above detection possible in the course of studying the effects of charging on our samples. Namely, the above aim can be accomplished by measuring electron kinetic energy changes (equivalent to surface potential changes) or sample (sample-to-ground) current changes during X-ray irradiation to detect charges caused by impurities or defects.