A method of degassing a thin layer and a method of manufacturing a silicon thin film includes applying microwaves to a silicon thin film deposited on a substrate to induce a resonance of impurities of H2, Ar, He, Xe, O2, and the like present in the silicon thin film so as to remove the impurities from the silicon thin film. A wavelength of the microwaves is equal to a natural frequency of an element of an object to be removed. According to a resonance of impurities induced by microwaves, the impurities can be very effectively removed from the silicon thin film so as to obtain a high quality silicon thin film. In particular, the microwaves are very suitable to be used in the manufacture of silicon thin films at low temperature.