<p>Two-dimensional (2D) BiOBr has garnered significant interest due to its exceptional optoelectronic properties. Currently, reported 2D BiOBr primarily exhibits n-type conductivity. However, in the field of optoelectronics, particularly within complementary metal oxide semiconductor (CMOS) integrated circuits, there is an urgent demand for high-quality p-type 2D semiconductors. In this study, we present the synthesis of high-quality, large-scale p-type 2D BiOBr crystals using chemical potential modulation chemical vapor deposition (CPMCVD). Notably, the conduction polarity of 2D BiOBr can be precisely controlled by modulating the oxygen chemical potential during the synthesis process. Density functional theory (DFT) calculations indicate that high oxygen chemical potential promotes the formation of bismuth vacancies in 2D BiOBr, resulting in p-type conductivity. Conversely, as the oxygen chemical potential decreases, oxygen vacancies become the predominant defects, leading to n-type BiOBr. Furthermore, both p-type and n-type high-performance field-effect transistors (FETs) based on 2D BiOBr have been fabricated. The p-type FETs exhibit a superior hole mobility of 26.28 cm² V⁻¹ s⁻¹ and on/off ratio exceeding 10⁴. The n-type FETs demonstrate an electron mobility of 59.59 cm² V⁻¹ s⁻¹, surpassing those reported for most n-type FETs. This breakthrough in the precise control of conduction polarity in 2D BiOBr using CPMCVD not only represents a significant milestone but also greatly expands its potential applications in advancing CMOS technology.</p>