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This paper reports a simple electrothermomechanical lumped element model (ETM-LEM) that describes the behavior of an electrothermal bimorph actuator. The ETM-LEM is developed by integrating an electrothermal LEM of a heater with a thermomechanical LEM of a bimorph actuator. This new LEM uses only one power source in both the electrical and thermal domains. The LEM provides a simple and accurate way of relating the output mechanical response of a bimorph actuator to the electrical inputs. The model shows that the tip angular rotation of the bimorph actuator is linearly proportional to its average temperature change. The LEM predicts a linear relationship between both the average temperature change and bimorph tip angular rotation versus voltage when operated above a certain voltage. The LEM is used to predict the rotation angle of a fabricated electrothermal bimorph micromirror in response to the electrical inputs and produces results that agree with finite element model simulations and experimental data within 15% for all measured parameters.