Making field effect transistors (FETs) on thin flake of single crystal isolated from layered materials was pioneered by the success of graphene. To overcome the difficulties of the zero band gap in graphene electronics, we report the fabrication of an electric double layer (EDL) transistor, a variant of FET, based on another layered material, MoS2. Using strong carrier tunability found in EDL coupled by ion movement, MoS2 transistor displayed an unambiguously ambipolar operation in addition to its commonly observed n-type transport. A high on/off ratio >104, large “ON” state conductivity of ∼mS, and a high reachable n
2D ∼ 1×1014 cm-2 confirmed the high performance transistor operation being important for application. The high-density carriers of both holes and electrons can drive the MoS2 channel to metallic states indicating that new electronic phases could be accessed using the protocol established in making EDL gated transistors on layered materials.