We investigate the resistive switching mechanism and the thermal stability in room temperature-fabricated nonvolatile memory consisting of W/TaOx/Pt. By comparing the chemical bonding of Ta 4f between high and low resistance states at W/TaOx and TaOx/Pt interfaces, the switching mechanism is confirmed to be dominated by the oxygen ions drift in the TaOx film. Besides, it is demonstrated that the resistive switching behavior is still dynamic and the resistance can be maintained at temperature as high as 510 K. We found that the resistive switching behavior of TaOx film exhibits little degradation even after annealed at 1273 K.