In this study, a high-speed and self-calibratable true random number generator (TRNG) is demonstrated based on a unified selector-RRAM device with dual switching modes. In fast selector mode (∼35 ns), the V th fluctuation is the entropy for the high-speed TRNG. However, V th has large device-to-device (D2D) variation, which leads to unstable switching probability. By adjusting the resistance of RRAM, the D2D variation of V th can be substantially regulated through self-calibration ($10\times \sigma/\mu$ improvement), enabling the reliable deployment of TRNG.