Abstract: A MOS transistor in a single-transistor memory cell having a locally thickened gate oxide, and a process for producing the transistor. The MOS transistor can be used as a selection transistor in a single-transistor memory cell having nitride spacers, or another spacer material acting as an oxidation barrier. The transistor also has a bird's beak in the gate oxide to reduce leakage currents. The production process enables the bird's beak to be produced before the nitride spacers are produced. The MOS transistor can be used in a DRAM, particularly as a selection transistor.