A plasma monitoring method using a sensor, the sensor having a substrate; a first electrode, the first electrode being a conductive electrode and formed on the substrate while being isolated from the substrate; an insulating film formed on the first electrode; a contact hole formed in the insulating film and having a depth from a surface of the insulating film to the first electrode; and a second electrode, the second electrode being a conductive electrode, formed on the surface of the insulating film, and faced to plasma during a plasma process, the plasma monitoring method including measuring and monitoring potentials of the first electrode and the second electrode or a potential difference between the first electrode and the second electrode during the plasma process is disclosed. A plasma monitoring system carrying out the plasma monitoring method is also disclosed.