Negative differential resistance (NDR) and memory phenomenon have been realized in current-voltage (I-V) characteristics of indium tin oxide/tris(8-hydroxyquinoline) aluminum/aluminum devices. The I-V curves have been divided into three operational regions that are associated with different working regimes of the devices: (i) bistable region, (ii) NDR region, and (iii) monotonic region. The bistable region disappeared after a couple of voltage sweeps from zero to a positive voltage. The bistable nature can be reinstated by applying a suitable negative voltage. The I-V characteristics have been explained in terms of space charge limited conduction. It has been found that injection of holes in these devices play an important role in NDR and resistive switching processes. Formation of nanofilamentary pathways and space charge field inhibition of injection elucidate the observed phenomenon well. (C) 2008 American Institute of Physics.