To realize multifunctional devices at the wafer scale, the growth process of monolayer (ML) 2D semiconductors must meet two key requirements: 1) growth of continuous and homogeneous ML film at the wafer scale and 2) controllable tuning of the properties of the ML film. However, there is still no growth method available that fulfills both of these criteria. Here, the first report is presented on the preparation of continuous and uniform ML MoS2 films through a two-step process at the wafer scale. Unlike in previous ML MoS2 film growth processes, the ML MoS2 film can be uniformly modulated across the wafer in terms of material structure and composition, exciton state, and electronic transport performance. A significant result is that the high-quality wafer-scale ML MoS2 films realize superior electronic performance compared to reported two-step-grown films, and it even matches or exceeds reported ML MoS2 films prepared by other processes. The transistor performance of the optimized ML film achieves a field effect mobility of 10 to 30 cm2 V−1 s−1, an on/off current ratio of about 107, and hysteresis as low as 0.4 V.