Hemt transistor including field plate regions and manufacturing process thereof

HEMT transistor (50; 100; 150) having a semiconductor body (52) forming a semiconductive heterostructure (54, 56); a gate region (60), of conductive material, arranged above and in contact with the semiconductor body (52); a first insulating layer (58) extending above the semiconductor body, laterally to the conductive gate region (60); a second insulating layer (62) extending above the first insulating layer (58) and the gate region (60); a first field plate region (84), of conductive material, extending between the first and the second insulating layers (58), laterally spaced from the conductive gate region (60); and a second field plate region (85), of conductive material, extending above the second insulating layer (62), vertically aligned with the first field plate region (84).