The substrate current and degradation behaviour of a novel trench LDD MOSFET, to be used as a high voltage device in the periphery of flash memories, is studied. At high drain voltage an unusual increase of the substrate current for high gate voltages is observed. Supported by device simulation this effect is attributed to the high series resistance of the device. The location of peak ionization rate is found to be shifted from the channel below the gate towards the trench LDD region. The degradation of linear current under several VGs stress conditions shows its maximum at gate voltages near the threshold voltage of the device. (C) 2002 Elsevier Science Ltd. All rights reserved.