Corona discharge air ionizers are widely used during quality control inspections to neutralize the static electricity on electronic devices because the electric field generated by static charge can lead to soft errors. However, an air ionizer may act as a source of noise, which can also lead to soft errors, because it creates a large number of ions that generate a high‐intensity electric field. The soft errors of a CMOS inverter in a large‐scale integration (LSI) were investigated in a minienvironment in which an AC corona discharge air ionizer was operated. The LSI mounted on a printed circuit board was placed 500 mm under the air ionizer, which was operated with a peak‐to‐peak voltage of 15 kV at frequencies of 1‐50 Hz. The noise in the output voltage, which is a source of soft errors, of the CMOS inverter decreased with increasing operating frequency. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.