The restorative effects of sulfur (S)-passivation through low-temperature (160 °C) post-S annealing on the performance and stability of monolayer molybdenum disulfide (MoS₂) field-effect transistors (FETs) are investigated. S-passivation suppresses S vacancies in the monolayer MoS₂ channel, restoring its intrinsic electrical and material properties and leading to enhancements in field-effect mobility from 8 to 95 cm^-2 V^-1 s^-1 and subthreshold swing from 0.21 to 0.10 V dec^-1. Hole-trapping associated with S vacancies results in the instability of the MoS₂ FETs under a negative bias stress, whereas S interstitials acting as electron trap states contribute to the instability of the S-passivated MoS₂ FETs under a positive bias stress. The effects of S-vacancy suppression on the charge-transport properties of the MoS₂ FETs are assessed by analyzing their activation energies and densities of states based on the reduction in defect states by S-passivation. An N-channel metal-oxide semiconductor inverter consisting of the S-passivated MoS₂ FETs exhibiting improved voltage gains is demonstrated for the first time, indicating its potential application in logic circuits based on monolayer transition-metal dichalcogenides.