Fabrication of large-area atomically thin transition metal dichalcogenides is of critical importance for the prepara-tion of new heterojunction-based devices. In this paper, we report the fabrication and optical investigation of large-scale chemical vapor deposition (CVD)-grown monolayer MoS2 and exfoliated few-layer GaS heterojunctions. As revealed by photoluminescence (PL) characterization, the as-fabricated heterojunctions demonstrated edge interaction between the two layers. The heterojunction was sensitive to annealing and showed increased interaction upon annealing at 300 ℃ under vacuum conditions, which led to changes in both the emission peak position and intensity resulting from the strong coupling interaction between the two layers. Low-temperature PL measurements further confirmed the strong coupling interaction. In addition, defect-related GaS luminescence was observed in our few-layer GaS, and the PL mapping provided evidence of edge interaction coupling between the two layers. These findings are interesting and provide the basis for creating new material systems with rich functionalities and novel physical effects.