A thermally responsive switch for protecting electric motors against overcurrent and overheating conditions includes a metallic receptacle having an elongated dome-shaped portion and an opening opposite to the dome-shaped portion, a metallic header plate secured to the one end of the receptacle so as to hermetically close the opening afterwards and having a through-aperture, a thermally responsive element disposed in the receptacle in parallel with the header plate and carrying a movable contact at one end, a rod terminal secured in the aperture of the header plate by an electrically insulating material filled in the aperture for hermetic sealing so that the terminal extends through the aperture, a fixed contact support disposed in the receptacle to be perpendicular to the terminal and having an end to which a fixed contact is secured, the support being connected at the other end to the end of the terminal projected into the receptacle, by solder, and a spring for urging the support so that it is disconnected from the terminal.