The epitaxial formation of metallic molybdenum carbide (Mo₂C, a 2D MXene material) is achieved via chemical conversion of molybdenum disulfide with thermal annealing under CH₄ and H_2. A fully converted metallic Mo₂C and Mo₂C/MoS₂ hybrid junctions could be provided with the adjusting of synthesis area of Mo₂C the thermal annealing period. Mo₂C film shows a metallic property as the outstanding electrode with a low sheet resistance (123.6 Ω/cm²) and carrier concentration of 5.84Х10¹³ /cm². Mo₂C/MoS₂ hybrid junctions display a low contact resistance (1.2 kΩ∙μm) and low Schottky barrier height (26 meV), indicating the material’s potential utility as a critical hybrid structural building block in future device applications. Mo₂C grows and forms a Mo₂C/MoS₂ hybrid structure were simulated by density functional theory calculations to model the mechanisms. The results show that Mo₂C conversion is initiated at the MoS₂ edge and undergoes sequential hydrodesulfurization and carbide conversion steps, and an atomically sharp interface with MoS₂ forms through epitaxial growth of Mo₂C. This work provides the area-controllable synthesis of a manufacturable MXene from a transition metal dichalcogenide (TMD) material and the formation of a metal/semiconductor junction structure. The present results will be of critical importance for future 2D heterojunction structures and functional device applications.