A representative embodiment of the invention provides a thermal actuator for a MEMS-based relay switch. The thermal actuator has an “active” arm that is movably mounted on a substrate. The “active” arm has (i) a thermal expansion layer and (ii) a resistive heater that is electrically isolated from the thermal expansion layer. The thermal expansion layer is adapted to expand in response to a temperature change induced by a control current flowing through the resistive heater, thereby bending the “active” arm and moving that arm with respect to the substrate. Due to the fact that mechanical and electrical characteristics of the “active” arm are primarily controlled by the thermal expansion layer and the resistive heater, respectively, those characteristics can be optimized independently to obtain better operating characteristics for MEMS-based relay switches of the invention compared to those attained in the prior art.