Electrothermal microactuators possess a number of desirable attributes including ease of fabrication and large force and displacement capabilities relative to other types of microactuators, but these performances come at the expense of large input energy and relatively low frequencies because of the time necessary to reach thermal equilibrium. These characteristics provide motivation for improving thermal actuator designs that are more energy efficient and better suited for high-frequency applications. To this end, models describing the combined electrothermal and thermomechanical behavior of thermal actuators are developed in this thesis. The temperature distribution of the actuator is analyzed and the influence of the actuator’s geometrical parameters on its force and displacement is studied. Steady-state and transient thermal responses of the actuator operating in air and a vacuum are investigated by creating finite-difference model with temperature-dependent parameters, this model allows temperatures throughout the actuator to be simulated as a function of time. Results demonstrate that the efficiency of the actuator can be improved significantly by operating in a vacuum environment and providing short-duration, high-current pulse inputs. A set of parametric studies and design changes are evaluated through thermomechanical models, strategies gained from modeling analysis result in significant improvements in operational efficiency of the thermal actuator.