Abstract: A thermal switch for automatically opening a circuit when the ambient temperature is increased to a predetermined level. A pair of conductor wires are arranged in side by side fashion with extremities extending in the same direction. A spring portion is included in at least one of the conductor wires to provide stored energy when the spring is biased into electrical contact with each other. A localized contact region is included in the conductor wire in the region below the spring portion but spaced upwardly from the associated extremities to create a lever arm. The extremities, contact region, lever arm and spring being encapsulated with a heat fusible material which biases the conductor wires into contact with each other and which is coated with a rigid insulating material to retain the conductor wires electrically insulated from each other except at the contact region.