A Field Effect Transistor (FET) having a source, drain, and gate disposed laterally along a surface of a semiconductor and a field plate structure: having one end connected to the source; and having a second end disposed between the gate and the drain and separated from the drain by a gap. A dielectric structure is disposed over the semiconductor, having: a first portion disposed under the second end of the field plate structure; and, a second, thinner portion under the gap.