The simplicity and prospect of energy efficiency of microelectromechanical systems (MEMS) resonator-based computing devices have captivated considerable research interest in recent years. Hence, they are being explored for ultra-low power computing machines, which are currently needed for internet-of-things (IoT) applications. Recently, there have been successful demonstrations of fundamental logic gates. However, the realization of complex multifunctional logic devices that involve multi-input and multi-output lines are facing challenges, such as the interconnections between multiple resonators and the limited controllability of the operating frequency. In this study, we demonstrate a 1:2 Demux combinational logic device with improved energy efficiency using the multi vibration modes of a single MEMS resonator. The MEMS device consists of three connected in-plane microbeams in the form of a U-shape structure. The actuation and modulation are based on electrostatic forces. The device shows actuation energy of 0.082 fJ and 0.91 fJ for output 1 and output 2, respectively, and switching energy per logic operation of 11.01 pJ for output 1 and 5.31 pJ for output 2. This indicates 75% decrease in switching energy per logic operation in comparison with the previously reported values for electrostatically actuated MEMS resonator-based computing devices.