<p>This paper presents OptGM, an optimized gate merging method designed to mitigate negative bias temperature instability (NBTI) in digital circuits. First, the proposed approach effectively identifies NBTI-critical internal nodes—those with a signal probability exceeding a predefined threshold. Next, based on the proposed optimized algorithm, the sensitizer gate—which drives the critical node—and the sensitive gate, which is fed by it, are merged into a new complex gate. This complex gate preserves the original logic while eliminating NBTI-critical nodes. Finally, to evaluate the effectiveness of OptGM, we assess it on several combinational and sequential benchmark circuits. Simulation results demonstrate that, on average, the number of NBTI-critical transistors (i.e., PMOS transistors connected to critical nodes), NBTI-induced delay degradation, and the total transistor count are reduced by 89.3%, 24%, and 7%, respectively. Furthermore, OptGM enhances performance per cost (PPC) by 12.8% on average, with minimal area overhead.</p>