Molybdenum disulfide (MoS₂) has been intensively investigated among the layered transition metal dichalcogenides (TMDs) due to its unique properties in various electronic and optoelectronic applications with different band gap energies from 1.29 to 1.9 eV as the number of layers is decreased. To control the MoS₂ layers, atomic layer etching (ALE) composed of a Cl radical adsorption step and a reacted-compound desorption step via a low-energy Ar⁺-ion exposure can be a highly effective technique to avoid inducing damage and contamination that occur during the cyclic steps. In this presentation, MoS₂ ALE is compared with conventional MoS2 plasma etching, and the MoS₂-ALE mechanism is reported with the results of an experiment and a simulation. Especially, using the ALE method, mono-layer/bi-layer MoS₂ field effect transistors (FETs) were fabricated their electrical characteristics were investigated and compared with the MoS₂ FETs fabricated with pristine mono-layer/bi-layer MoS₂. In addition, mono-/bi-layer lateral-heterojunction device was fabricated using ALE technique after PR patterning of bilayer MoS₂.