  The Kondo lattice, describing a matrix of local magnetic moments coupled via
spin-exchange interactions to itinerant conduction electrons, is a prototype of
strongly correlated quantum matter. Traditionally, Kondo lattices are realized
in intermetallic compounds containing lanthanide or actinide. The complex
electronic structure and limited tunability of both the electron density and
exchange interactions in these bulk materials pose significant challenges to
study Kondo lattice physics. Here, we report the realization of a synthetic
Kondo lattice in AB-stacked MoTe2/WSe2 moir\'e bilayers, where the MoTe2 layer
is tuned to a Mott insulating state, supporting a triangular moir\'e lattice of
local moments, and the WSe2 layer is doped with itinerant conduction carriers.
We observe heavy fermions with a large Fermi surface below the Kondo
temperature. We also observe destruction of the heavy fermions by an external
magnetic field with an abrupt decrease of the Fermi surface size and
quasiparticle mass. We further demonstrate widely and continuously gate-tunable
Kondo temperatures through either the itinerant carrier density or Kondo
interaction. Our study opens the possibility of in-situ access to the rich
phase diagram of the Kondo lattice with exotic quantum criticalities in a
single device based on semiconductor moir\'e materials
