Charge-trapping memory devices based on two-dimensional (2D) material heterostructures possess an atomically thin structure and excellent charge transport capability, making them promising candidates for next-generation flash memories to achieve miniaturized size, high storage capacity, fast switch speed, and low power consumption. Here, we report a nonvolatile floating-gate memory device based on an ReS₂/boron nitride/graphene heterostructure. The implemented ReS₂ memory device displays a large memory window exceeding 100 V, leading to an ultrahigh current ratio over 10⁸ between programming and erasing states. The ReS₂ memory device also exhibits an ultrafast switch speed of 1 μs. In addition, the device can endure hundreds of switching cycles and shows stable retention characteristics with ∼40% charge remaining after 10 years. More importantly, taking advantage of its anisotropic electrical properties, a single ReS₂ flake can achieve direction-sensitive multi-level data storage to enhance the data storage density. On the basis of these characteristics, the proposed ReS₂ memory device is potentially able to serve the entire memory device hierarchy, meeting the need for scalability, capacity, speed, retention, and endurance at each level.