  The presence of a direct band gap and an ultrathin form factor has caused a
considerable interest in two-dimensional (2D) semiconductors from the
transition metal dichalcogenides (TMD) family with molybdenum disulphide (MoS2)
being the most studied representative of this family of materials. While
diverse electronic elements, logic circuits and optoelectronic devices have
been demonstrated using ultrathin MoS2, very little is known about their
performance at high frequencies where commercial devices are expected to
function. Here, we report on top-gated MoS2 transistors operating in the
gigahertz range of frequencies. Our devices show cutoff frequencies reaching 6
GHz. The presence of a band gap also gives rise to current saturation, allowing
power and voltage gain, all in the gigahertz range. This shows that MoS2 could
be an interesting material for realizing high-speed amplifiers and logic
circuits with device scaling expected to result in further improvement of
performance. Our work represents the first step in the realization of
high-frequency analog and digital circuits based on two-dimensional
semiconductors.
