<p>The presence of defects such as cracks can accelerate the pull-in phenomenon in microelectromechanical systems (MEMS). Therefore, it is essential to have a reliable index to detect cracks for monitoring the condition of these systems. This study primarily focuses on the dynamic pull-in instability induced by high-frequency voltage excitation, rather than static pull-in conditions. It has been demonstrated that applying high-frequency voltage excitation within a specific interval, known as the stability region, can prevent the pull-in phenomenon. This research investigates the impact of crack parameters (depth and location) on the stability region in post-pull-in situations of microbeams. The findings reveal that these stability regions vary for different types of cracks, suggesting their potential utility as a novel index for detecting microstructure crack parameters. To analyze these regions, the cracked microbeam is demonstrated as a one-degree-of-freedom system comprising mass-spring-damper elements, and the motion equation is derived. Using the direct partition of motion, the equation is decomposed into fast and slow dynamics. The effect of cracks on the average vibration position of the microbeam is explored for alternating current (AC) excitation with varying voltage and frequency amplitudes. The study shows that as the crack moves closer to the support or its depth increases, the stability region area decreases, and the pull-in phenomenon can be mitigated at smaller voltage and frequency amplitudes. This new index and an updating model can be used to extract crack parameters, which is valuable for monitoring the condition of MEMS sensors in dynamic environments.</p>