Superconductivity in monolayer tungsten disulfide (2H-WS2) is achieved by strong electrostatic electron doping of an electric double-layer transistor (EDLT). Single crystals of WS2 are grown by a scalable method - chemical vapor deposition (CVD) on standard Si/SiO2 substrate. The monolayers are identified by both AFM and color-coding techniques. The EDLT device based on single-layer WS2 shows ambipolar transfer characteristics indicating a semiconducting nature of the material. Metallic transport on the electron side evolves into superconductivity with critical temperature T-c = 3.15 K.