Recent discoveries in the field of graphene‐based heterostructures have led to the demonstration of high‐performance photodetectors. However, the studies to date have been largely limited to the heterojunction with a Schottky barrier, restricted by an inevitable compromise between photoresponsivity and photodetectivity. Here, a new class of graphene‐based tunneling photodetectors is introduced by inserting the Al ₂ O ₃ tunneling layer between silicon and graphene. The photocarriers can tunnel through the designed insulator layer which simultaneously blocks the dark current, thus maintaining high photodetectivity with desirable photoresponsivity. We further modulate the thickness of the Al ₂ O ₃ layer to explore the tunneling mechanism for the photocarriers, in which a photoresponsivity of 0.75 A/W, a high current ratio of 4.8 × 10 ³ and a photodetectivity of 3.1 × 10 ¹² Jones are obtained at a 13.3‐nm‐thick Al ₂ O ₃ layer. In addition, the fabrication process is compatible with conventional semiconductor processing, providing further flexibility to large‐scale integrated photodetectors with high performance.