Moiré materials provide a highly tunable platform to explore the strongly correlated electron phenomena. A Mott insulator with local magnetic moments has been realized in semiconductor moiré materials at half-filling of the moiré band. In this talk, I will describe the realization of a synthetic Kondo lattice in AB-stacked MoTe2/WSe2 moiré bilayers, where the MoTe2 layer is tuned to a Mott insulating state, supporting a triangular moiré 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 and the destruction of the heavy fermions by an external magnetic field with an abrupt decrease of the Fermi surface size and quasiparticle mass. I will also demonstrate a density-tuned Kondo breakdown transition and the emergence of ferromagnetism.