The present disclosure relates to semiconductor structures and, more particularly, to silicon controlled rectifiers with field plate structures and methods of manufacture. The structure includes: a plurality of wells of a first type in a semiconductor substrate; a well of a second type in the semiconductor substrate, the well of the second type surrounding the plurality of wells of the first type; an isolation structure surrounding the plurality of wells of the first type, the isolation structure isolating the well of the second type from the plurality of wells of the first type; and a plurality of field plates on the isolation structure, the plurality of field plates surround the plurality of wells of the first type.