An emerging electronic material as one of transition metal dichalcogenides (TMDCs), tungsten disulfide (WS 2) can be exfoliated as an atomically thin layer and can compensate for the drawback of graphene originating from a gapless band structure. A direct bandgap, which is obtainable in single-layer WS 2 , is an attractive characteristic for developing optoelectronic devices, as well as field-effect transistors. However, its relatively low mobility and electrical characteristics susceptible to environments remain obstacles for the use of device materials. Here, we demonstrate remarkable improvement in the electrical characteristics of single-layer WS 2 field-effect transistor (SL-WS 2 FET) using chemical vapor deposition (CVD)-grown hexagonal BN (h-BN). SL-WS 2 FET sandwiched between CVD-grown h-BN films shows unprecedented high mobility of 214 cm 2 /Vs at room temperature. The mobility of a SL-WS 2 FET has been found to be 486 cm 2 /Vs at 5 K. The ON/OFF ratio of output current is ~10 7 at room temperature. Apart from an ideal substrate for WS 2 FET, CVD-grown h-BN film also provides a protection layer against unwanted influence by gas environments. The h-BN/SL-WS 2 /h-BN sandwich structure offers a way to develop high-quality durable single-layer TMDCs electronic devices. Despite all its advantages as an important material for atomically thin layered electronic device applications , graphene cannot be used as a promising material for active channel in field-effect transistors (FETs) because of the absence of a bandgap. Bandgap in graphene can be introduced by patterning into nanoribbons