With reference to FIGS. 2A and 2B the differences between a transistor cell of the stripe design and a transistor cell of the trench needle design is explained in more detail. FIG. 2A shows a unit cell of the stripe design while FIG. 2B illustrates a unit cell of the trench needle design.

The transistor cell of FIG. 2A is formed in a semiconductor substrate 200 having a first side 201 and the second side. The first side 201 defines the main side or surface of the semiconductor substrate 200 while the second side defines a side opposite to the first side 201. The stripe design includes a long and deep field plate trench 230 which is formed to extend from the first side 201 of the semiconductor substrate into the semiconductor substrate 100. The field plate trench 230 has a stripe shape when seen in plain projection onto the first side 201 of the semiconductor substrate 200. Each field plate trench 230 includes a field electrode 231 which is indicated by phantom lines in FIG. 2A. The field electrode 231 has a plate-like shape parallel to the longitudinal extension of the field plate trench 230. A thick field oxide 232 electrically insulates the field electrode 231 from the semiconductor substrate 200. Next to and parallel with the field plate trench 230 is running a cell mesa region 220 extending up to the first side 201 of the semiconductor substrate 200.