Integrated circuits (ICs), the backbone of modern electronics and optoelectronics, face scaling and efficiency bottlenecks due to intrinsic limitations of silicon, whereas hexagonal boron nitride (hBN) emerges as a compelling alternative for next-generation nanoelectronics with its exceptional physical properties. However, realising semiconducting behaviour in hBN to use it as an active channel while preserving its intrinsic stability and interface quality remains a significant challenge due to its ultra-wide bandgap. Here, they demonstrate that tailoring the defect structure of hBN enables band structure tuning, resulting in a marked conductivity improvement. By introducing sulfur (S) as a transient dopant during chemical vapor deposition (CVD), we facilitate tin (Sn) incorporation into hBN through a S-mediated substitution pathway. First-principles calculations reveal that the S-induced intermediate configuration (hBN: SNVB) significantly lower the formation energy for Sn substitution, resulting in the creation of mid-gap states that enhance carrier concentration and mobility. This strategy achieves robust Sn