||Two dimensional (2D) transition metal dischalcogenides (TMDCs) have attracted great attention as low dimensional semiconducting materials. 2D TMDCs have shown exotic electronic and optical properties: Indirect-to-direct bandgap transition with reducing number of layers, high carrier mobility and strong spin-orbit coupling due to their broken inversion symmetry. Despite of their remarkable properties, however, the studies on the synthesis of 2D TMDCs are still showing various limitations in layer controllability, large area uniformity. Thus, the focus of our research is to understand and control the growth of 2D TMDCs based on atomic layer deposition (ALD) and to apply to electronic and optical devices. In this talk, I will present the synthesis of 2D TMDCs using ALD process. Furthermore, potential applications of 2D TMDCs, including field effect transistors (FET), gas sensor, PN diode, and photodetector, will be introduced.