Atomically thin MoS₂ single crystals have a two-dimensional structure and exhibit semiconductor properties, and have therefore recently been utilized in electronic devices and circuits. In this study, we have fabricated a field effect transistor (FET), using a CVD-grown, 3 nm-thin, MoS₂ single-crystal as a transistor channel after transfer onto a SiO2/Si substrate. The MoS2 FETs displayed n-channel characteristics with an electron mobility of 0.05 cm²/V-sec, and a current on/off ratio of ION/IOFF?5×10⁴. Application of bottom-gate voltage stresses, however, increased the interface charges on MoS2/SiO₂, incurred the threshold voltage change, and degraded the device performance in further measurements. Exposure of the channel to UV radiation further degraded the device properties.