Single-crystal wafers of p-type two-dimensional (2D) semiconductors are highly desired for next-generation electronics. However, p-type 2D semiconductors remain scarce, and achieving wafer-scale monolayer single crystals of such materials is even more challenging. Here we report the wafer-scale growth of p-type semiconducting monolayer MoSi2N4 single crystals on Cu (111) foils with prestored Mo and Si atoms. The <110> steps on Cu (111) guide the nucleation and unidirectional orientation of monolayer MoSi2N4 domains, enabling their seamless stitching into a continuous single-crystal film. The resulting MoSi2N4 exhibits exceptional quality, with an intrinsic mobility of 154 cm2 V−1 s−1. Field-effect transistor arrays fabricated from this material deliver excellent electrical performance, including an on/off ratio of ~3.8 ± 1.4 × 106 and an on-state current density up to ~17.96 μA μm−1 (1 μm channel length), along with superior stability compared with monolayer WSe2-based counterparts. Furthermore, this versatile growth strategy also enables the fabrication of wafer-scale monolayer WSi2N4 single crystals. This work establishes a promising p-type 2D semiconductor platform for future integrated circuits.