The introduction of 3D-VNAND structure has led to a significant increase in bit density, and the evolution to Cell Over Peripheral circuits (COP) has further accelerated this trend. However, the cell fabrication process following the peripheral transistor process can significantly impact the characteristics of peripheral transistors, posing a challenge in achieving high performance and reliability in VNAND flash memory devices. In this article, we present the index of Hydrogen-induced Boron penetration, so called HBp-index, a novel quantitative model that explains the combination effect of hydrogen and process heat on peripheral transistors in 3D NAND flash memory. We observed the index linearly matched with the change of the electrical characteristics of the transistors for various heat processes. Furthermore, it was found from the result that hydrogen induced by cell process caused degradation of HCI by 42mV and NBTI by 22mV, consistent with previous papers [5], [6].