Successive sparks in high-density plasma were analyzed using various real-time monitoring systems, such as electromagnetic field sensors and on-wafer sensors. Electron density decreases at the moment the sparking occurs because a large number of electrons flow to the chamber wall and the wafer surface. Due to the potential fluctuation of the plasma, other sparks occur successively during recovery to the stable plasma. The successive sparks sometimes continue for a few milliseconds. Based on these findings, the authors found that electromagnetic field sensors and on-wafer sensors are very effective tools for real-time monitoring of successive sparks.