Two-dimensional layered semiconductors such as molybdenum disulfide (MoS₂) have attracted tremendous interest as a new class of electronic materials. However, there are considerable challenges in making reliable contacts to these atomically thin materials. Here we present a new strategy by using graphene as the back electrodes to achieve ohmic contact to MoS₂. With a finite density of states, the Fermi level of graphene can be readily tuned by a gate potential to enable a nearly perfect band alignment with MoS₂. We demonstrate for the first time a transparent contact to MoS₂ with zero contact barrier and linear output behavior at cryogenic temperatures (down to 1.9 K) for both monolayer and multilayer MoS₂. Benefiting from the barrier-free transparent contacts, we show that a metal–insulator transition can be observed in a two-terminal MoS₂ device, a phenomenon that could be easily masked by Schottky barriers found in conventional metal-contacted MoS₂ devices. With further passivation by boron nitride (BN) encapsulation, we demonstrate a record-high extrinsic (two-terminal) field effect mobility up to 1300 cm²/(V s) in MoS₂ at low temperature.