A thermal cut-off device includes a plastic base, two electrodes, a temperature sensing element, and a plastic cover that fits over the base. The temperature sensing element is curved downward, and may be a bimetal or a trimetal. When the device is subject to an over-temperature condition, the orientation of the curve flips such that the temperature sensing element is then curved upward. When the temperature sensing element is curved upward, it lifts an arm of one of the electrodes, which severs the electrical connection between the electrodes. In this manner the device shuts off during an over-temperature condition in order to protect the circuit in which the device is installed. To prevent corrosion of the temperature sensing element, a first moisture insulation layer is applied to the outer surface of the thermal cut-off device. The moisture insulation layer may be an epoxy adhesive or a UV/visible light-cured adhesive or light/heat cured adhesive. In some embodiments, a second moisture insulation layer is formed on the surface of the temperature sensing element.