The present invention discloses a microwave plasma generator which includes a chamber, a conductive inorganic substance, a trace gas and a microwave source. The conductive inorganic substance and the trace gas are housed in the chamber with an inner pressure about 0.001.about.10 torr. By irradiating the conductive inorganic substance and exciting the trace gas, clean and uniform plasma will be generated. The plasma generator of this invention is easily operated and can be applied to semiconductor manufacturing processes, for example, material modification, etching/cleaning, roughing and ion doping/hybrid.