A large area (20 mm × 20 mm) of single-crystalline monolayer hBN without anymicroscopic defects (grain boundaries, twins, etc.) was successfully synthesized by MOCVD at littleabove the atmospheric pressure (770 torrs). It was primarily possible due to utilizing the largearea and single-crystalline Cu as a substrate prepared by a contactless heat treatment method toprevent any heat-related stress to the specimen. With carefully controlled and well-organizedexperiments, it was found that a slow increase in temperature is more critical than long-time heattreatment. Secondly, heat treatment at 1083°C after a quick temperature reduction from 1084°C to1083°C within 1 min is another key condition to obtain a smooth surface for the growth ofsingle-crystalline Cu without any defects. Microstructural studies of synthesized hBN were carriedout by X-ray diffraction, optical microscopy, scanning electron microscopy, and transmissionelectron microscopy.