Here we use triple-cation metal-organic halide perovskite single crystals for the transistor channel of a flash memory device. Moreover, we design and demonstrate a 10 nm thick single-layer nanofloating gate. It consists of a ternary blend of two organic semiconductors, a p-type polyfluorene and an n-type fullerene that form a donor:acceptor interpenetrating network that serves as the charge storage unit, and of an insulating polystyrene that acts as the tunneling dielectric. Under such a framework, we realize the first non-volatile flash memory transistor based on a perovskite channel. This simplified, solution-processed perovskite flash memory displays unique performance metrics such as a large memory window of 30 V, an on/off ratio of 9 × 107, short write/erase times of 50 ms, and a satisfactory retention time exceeding 106 s. The realization of the first flash memory transistor using a single-crystal perovskite channel could be a valuable direction for perovskite electronics research.