A method of manufacturing a flexible device including a two-dimensional (2D) material, e.g., graphene, includes forming a dielectric layer on a first substrate, forming a two-dimensional (2D) material layer on the dielectric layer; forming a pattern in the 2D material layer, forming a second substrate on the dielectric layer and the 2D material layer, the first substrate including a flexible material, removing the first substrate, and forming a source electrode, a drain electrode, and a gate electrode on the dielectric layer.