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Abstract The formation of heterojunction within solid‐state devices enables them with eventually high performances, but provides a challenge for material synthesis and device fabrication because strict conditions such as lattice match are needed. Herein, we show a facile method to fabricate a van der Waals (vdW) heterojunction between two‐dimensional (2D) bismuth oxyselenide (Bi2O2Se) and graphene, during which the graphene is directly transferred to the Bi2O2Se and served as a low‐contract‐resistant electrode with small work function mismatch (~50 meV). As an optoelectronic device, the Bi2O2Se/graphene vdW heterojunction allows for the efficient sensing toward 1200‐nm incident laser. Regarding the application of field‐effect transistors (FETs), the short‐channel (50 nm) sample can be synthesized by utilizing these two 2D materials (ie, channel: Bi2O2Se; drain/source terminal: graphene) and the n‐type characteristic can be observed with the accordant field modulation. It is confirmed that we show a simple way to prepare the vdW heterojunction which is aiming to the high‐performance applications among optoelectronics and FETs.