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 .