A method of forming a semiconductor structure, the method comprising: forming a buried region in a substrate, the substrate having a first conductivity type, the buried region having a second conductivity type; growing an epitaxial layer on the substrate, the epitaxial layer having a top surface and the first conductivity type, the buried region touching and lying below a portion of the epitaxial layer; forming a shallow trench isolation structure in the top surface of the epitaxial layer to extend down into the epitaxial layer; forming an inner deep trench isolation structure in the top surface of the epitaxial layer to extend down into the epitaxial layer, the inner deep trench isolation structure laterally surrounding the shallow trench isolation structure; forming an outer deep trench isolation structure in the top surface of the epitaxial layer to extend down into the epitaxial layer, the outer deep trench isolation structure laterally surrounding the inner deep trench isolation structure; and forming a doped region in the top surface of the epitaxial layer to extend down into the epitaxial layer and touch the buried region, the doped region having the second conductivity type, touching the inner and outer deep trench isolation structures (312, 314), and laterally surrounding the portion of the epitaxial layer, wherein a plurality of spaced-apart regions (512, 514) of the second conductivity type are formed which touch the inner and outer deep trench isolation structures and lie between the inner and outer deep trench isolation structures and the doped region is formed by diffusing the spaced apart regions laterally together thereby reducing the maximum width of the doped region below the deep trench isolation structures. forming a buried region in a substrate, the substrate having a first conductivity type, the buried region having a second conductivity type; growing an epitaxial layer on the substrate, the epitaxial layer having a top surface and the first conductivity type, the buried region touching and lying below a portion of the epitaxial layer; forming a shallow trench isolation structure in the top surface of the epitaxial layer to extend down into the epitaxial layer; forming an inner deep trench isolation structure in the top surface of the epitaxial layer to extend down into the epitaxial layer, the inner deep trench isolation structure laterally surrounding the shallow trench isolation structure; forming an outer deep trench isolation structure in the top surface of the epitaxial layer to extend down into the epitaxial layer, the outer deep trench isolation structure laterally surrounding the inner deep trench isolation structure; and forming a doped region in the top surface of the epitaxial layer to extend down into the epitaxial layer and touch the buried region, the doped region having the second conductivity type, touching the inner and outer deep trench isolation structures (312, 314), and laterally surrounding the portion of the epitaxial layer, wherein a plurality of spaced-apart regions (512, 514) of the second conductivity type are formed which touch the inner and outer deep trench isolation structures and lie between the inner and outer deep trench isolation structures and the doped region is formed by diffusing the spaced apart regions laterally together thereby reducing the maximum width of the doped region below the deep trench isolation structures.