AbstractResistive random access memory (RRAM) with ultrafast and multilevel switching is extremely promising for next‐generation nonvolatile memory. Here, ultrafast unipolar resistive switchings (≈540 ps) with high off/on resistance ratio (≈104) are obtained in yttrium iron garnet Y3Fe5O12 (YIG)‐based resistive memory on n‐Si substrate. The sub‐nanosecond operation is also successfully performed up to 85 °C with an off/on resistance ratio of ≈103. In addition, by using different compliance currents for the set process, five discrete resistance levels with ultrafast switchings among them are achieved and the multilevel states show reliable retention (>104 s). The large, stable, reproducible, and reliable switching behaviors of the Au/YIG/n‐Si RRAM cell shows its great potential for ultrafast multilevel memory applications.