The present thermal fuse comprises an electrically and thermally conductive housing for hermetically sealing the switching parts and a fusible, temperature sensitive pellet in said housing. The pellet is preferably molded to have a cylindrical shape or body provided with one cavity or several cavities and assembled in the housing, whereby the outside pellet surface contacts the inner surface of the housing. The cavity or cavities take up about 5 to 50 percent of the whole cross sectional area of the pellet. The pellet is made of a mixture of organic and inorganic substances preferably so as to accelerate the fusing function of the pellet when the temperature rises above the melting point of the major component of the organic materials. The cavity or cavities of the pellet greatly facilitate a large and rapid shrinkage in volume and the addition of inorganic substance provides a large thermal conductivity of the pellet, whereby a rapid and exact fuse action is accomplished.