An integrated circuit chip includes: a plurality of parallel wells of alternated conductivity types formed in the upper portion of a semiconductor substrate of a first conductivity type; in each well of the first type, a plurality of MOS transistors having a channel of the second conductivity type, and in each well of the second type, a plurality of MOS transistors having a channel of the first type, transistors of neighboring wells being inverted-connected; and a device of protection against attacks, including: a layer of the second type extending under said plurality of wells, from the lower surface of said wells; and regions of lateral insulation between the wells, said regions extending from the upper surface of the wells to said layer.