Monolayer (ML) transition metal dichalcogenides are novel, gapped two-dimensional materials with unique electrical and optical properties. Toward device applications, we consider MoS 2 layers on dielectrics, in particular in this work, the effect of vacancies on the electronic structure. In density-functional based simulations, we consider the effects of near-interface O vacancies in the oxide slab, and Mo or S vacancies in the MoS 2 layer. Band structures and atom-projected densities of states for each system and with differing oxide terminations were calculated, as well as those for the defect-free MoS 2-dielectrics system and for isolated dielectric layers for reference. Among our results, we find that with O vacancies, both the Hf-terminated HfO 2–MoS 2 system, and the O-terminated and H-passivated Al 2 O 3–MoS 2 systems appear metallic due to doping of the oxide slab followed by electron transfer into the MoS 2, in manner analogous to modulation doping. The n-type doping of ML MoS 2 by high-k oxides with oxygen vacancies then is experimentally demonstrated by electrically and spectroscopically characterizing back-gated ML MoS 2 field effect transistors encapsulated by oxygen deficient alumina and hafnia.