<p>The development of compatible p-type and n-type pairs within the same matrix is essential for high-efficiency thermoelectric devices. While substantial advancements have been achieved in the figure of merit for p-type GeSe, achieving high-performance n-type GeSe remains a formidable challenge due to the strong covalent bonding in the orthorhombic phase, which restricts dopant solubility, induces low cationic vacancy formation energy, and hence obstructs the critical p-to-n type transition. Here, we utilize AgBiTe₂ alloying to facilitate the transition of GeSe from its covalently bonded orthorhombic phase to the metavalently bonded cubic phase, thus enhancing dopability and enabling precise manipulation of point defects. The superior solubility of Bi relative to Ag in the GeSe matrix generates a dominant donor effect from Bi³⁺, while the concentration of anionic vacancies, particularly Te vacancies, progressively outbalances that of cationic vacancies, both of which accelerate the successful p-to-n type conversion of GeSe. By introducing a slight Te deficiency to optimize electron concentration, we attain a record-breaking <i>zT</i> of 0.51 at 723 K in n-type cubic (GeSe)_0.5(AgBiTe_1.93)_0.5. This work not only unveils a promising route for high-performance n-type GeSe but also provides valuable insights into the interplay of chemical bonding, phase structure, dopability, and point defects in chalcogenides.</p>