In DRAM memory cells, individual memory cells are isolated from one another by an isolation trench (STI). In such a case, a vertical transistor is formed by the isolation trench as SOI transistor because its channel region is isolated from a substrate by the isolation trench. A vertical transistor that is used, for example, in a DRAM memory cell and a method for making the transistor includes connecting the channel region of the vertical transistor to the substrate by disposing a conductive layer in the isolation trench between a lower insulation filling and an upper insulation filling.