A structure comprising a field-effect transistor provided along an upper surface of a semiconductor body having body material doped with semiconductor dopant of a first conductivity type so as to be of the first conductivity type, the transistor comprising: a channel zone of the body material; first and second source/drain ("S/D") zones situated in the semiconductor body along its upper surface, laterally separated by the channel zone, and being of a second conductivity type opposite to the first conductivity type so as to form respective pn junctions with the body material such that (a) each pn junction reaches a maximum depth below the body's upper surface, (b) the body material extends laterally under both S/D zones, (c) the dopant of the first conductivity type is present in both S/D zones and has a concentration which locally reaches a subsurface maximum concentration at a subsurface maximum concentration location extending laterally below all of each of the channel and S/D zones, decreases by at least a factor of 10 in moving upward from the subsurface maximum concentration location along a selected vertical location through a specified one of the S/D zones to the body's upper surface, decreases monotonically and inflectionlessly in moving from the subsurface maximum concentration location along the selected vertical location to the pn junction for the specified S/D zone, and has at least a non-zero background value throughout all of each S/D zone, and (d) the subsurface maximum concentration location occurs no more than 10 times deeper below the body's upper surface than the maximum depth of the pn junction for the specified S/D zone; a gate dielectric layer overlying the channel zone; and a gate electrode overlying the gate dielectric layer above the channel zone, each S/D zone comprising a main S/D portion and a more lightly doped lateral S/D extension laterally continuous with the main S/D portion and extending laterally under the gate electrode such that the channel zone is terminated by the S/D extensions along the body's upper surface; wherein the concentration of the dopant of the first conductivity type decreases by less than a factor of 10 in moving from the subsurface maximum concentration location along the selected vertical location to the pn junction for the specified S/D zone. a channel zone of the body material; first and second source/drain ("S/D") zones situated in the semiconductor body along its upper surface, laterally separated by the channel zone, and being of a second conductivity type opposite to the first conductivity type so as to form respective pn junctions with the body material such that (a) each pn junction reaches a maximum depth below the body's upper surface, (b) the body material extends laterally under both S/D zones, (c) the dopant of the first conductivity type is present in both S/D zones and has a concentration which locally reaches a subsurface maximum concentration at a subsurface maximum concentration location extending laterally below all of each of the channel and S/D zones, decreases by at least a factor of 10 in moving upward from the subsurface maximum concentration location along a selected vertical location through a specified one of the S/D zones to the body's upper surface, decreases monotonically and inflectionlessly in moving from the subsurface maximum concentration location along the selected vertical location to the pn junction for the specified S/D zone, and has at least a non-zero background value throughout all of each S/D zone, and (d) the subsurface maximum concentration location occurs no more than 10 times deeper below the body's upper surface than the maximum depth of the pn junction for the specified S/D zone; a gate dielectric layer overlying the channel zone; and a gate electrode overlying the gate dielectric layer above the channel zone, each S/D zone comprising a main S/D portion and a more lightly doped lateral S/D extension laterally continuous with the main S/D portion and extending laterally under the gate electrode such that the channel zone is terminated by the S/D extensions along the body's upper surface; wherein the concentration of the dopant of the first conductivity type decreases by less than a factor of 10 in moving from the subsurface maximum concentration location along the selected vertical location to the pn junction for the specified S/D zone.