Abstract: A surface mountable electronic device has a case with an opening, an electronic element contained inside the case such as a thermistor or a varistor that generates heats when in operation, a plurality of elongated spring terminals supporting this electronic element elastically together and each sandwiching a wall of the case both from inside and outside at a peripheral edge part of the wall at its opening, and a lid attached to the case so as to close up its opening except where the spring terminals pass through the opening. Grooves are preferably formed at peripheral edge parts of the wall where the spring terminals are fitted, contacting the wall such that heat generated by the electronic element during its operation and propagating through the spring terminals can be effectively conducted to the main body of the case and diverted from its soldered junctures with a circuit board.