A method of detecting whether a microelectromechanical system (MEMS) device is hermetic includes applying at least three voltage differences between a movable part and a sensor electrode of the MEMS device to measure at least three effective capacitances, calculating a capacitance-to-voltage curve and an offset voltage of the MEMS device according to the at least three effective capacitances; and determining whether the offset voltage is within a predetermined range to determine whether MEMS device is hermetic.