We demonstrated that an Al/p-type amorphous silicon (p-a-Si)/Al switching device exhibits stable, nonvolatile resistive switching characteristics as well as reliable data retention at 85 degrees C. It is directly observed that the conducting filament is created after electroforming and incorporates the top metal migrated or diffused into a-Si layer. In addition, by analyzing the constitution of the conducting filament, we investigated the microscopic nature of the conducting filament. These results suggest that the Al/p-a-Si/Al device has potential for future nonvolatile memory applications.