  Crystalline two-dimensional (2D) superconductors with low carrier density are
an exciting new class of materials in which superconductivity coexists with
strong interactions, the effects of complex topology are not obscured by
disorder, and electronic properties can be strongly tuned by electrostatic
gating. Very recently, two such materials, 'magic-angle' twisted bilayer
graphene and monolayer $T_d$-WTe$_2$, have been reported to show
superconductivity at temperatures near 1 K. Here we report superconductivity in
semimetallic monolayer $T_d$-MoTe$_2$. The critical temperature $T_\textrm{c}$
reaches 8 K, a sixty-fold enhancement as compared to the bulk. This anomalous
increase in $T_\textrm{c}$ is only observed in monolayers, and may be
indicative of electronically mediated pairing. Reflecting the low carrier
density, the critical temperature, magnetic field, and current density are all
tunable by an applied gate voltage, revealing a superconducting dome that
extends across both hole and electron pockets. The temperature dependence of
the in-plane upper critical field is distinct from that of $2H$ transition
metal dichalcogenides (TMDs), consistent with a tilted spin texture as
predicted by \textit{ab initio} theory.
