Disclosed herein are a microwave probe capable of precisely detecting a plasma state in a plasma process, a plasma monitoring system including the probe, and a method of fabricating a semiconductor device using the system. The microwave probe includes a body extending in one direction and a head which is connected to one end of the body and has a flat plate shape. In addition, in the plasma process, the microwave probe is non-invasively coupled to a chamber such that a surface of the head contacts an outer surface of a viewport of the chamber, and the microwave probe applies a microwave into the chamber through the head and receives signals generated inside the chamber through the head.