To further reduce power dissipation, suppressing the subthreshold swing (SS) to overcome the physical limit of 60 mV dec(-1) is demanded in metal-oxide-semiconductor field effect transistors (MOSFETs). Here, we theoretically propose that the unique Dirac point and the strong density of state peak of monolayer Ag2S can sufficiently suppress the thermal tail of injected electrons for a steep-slope MOSFET. The 12 nm-gate-length n-type Ag2S MOSFET brings the SS down to 30 mV dec(-1) with a high on-state current of 2258 mu A mu m(-1), fulfilling the International Roadmap for Devices and Systems requirements for 2028 both in high-performance and low-power applications. Additionally, the sub-10 nm n-type Ag2S MOSFETs are also evaluated by the International Technology Roadmap for Semiconductors for high-performance devices and satisfy the requests until the gate length scales down to 5 nm. Our results suggest that monolayer Ag2S is a promising channel alternative for steep-slope transistors in next-generation electronics.