Semiconductor structures and methods of forming the same

A method of forming a semiconductor structure, comprising:

• providing a substrate;
• forming a source structure and a drain structure on the substrate;
• forming a gate structure on the substrate and between the source structure and the drain structure;
• forming a first field plate on the substrate;
• forming a first oxide layer between the substrate and the first field plate;
• forming a second field plate on the first field plate, wherein the second field plate is closer to the drain structure than the first field plate;
• forming a planarized second oxide layer between the first oxide layer and the second field plate;
• and
• forming a third field plate on the second field plate, wherein the third field plate is closer to the drain structure than the second field plate, wherein an end of the third field plate close to the source structure is closer to the drain structure than an end of the second field plate close to the source structure, and the end of the second field plate close to the source structure is closer to the drain structure than an end of the first field plate close to the source structure.