An embodiment of a nonvolatile-memory device includes: a body accommodating at least a first semiconductor well and a second semiconductor well; an insulating structure; and at least one nonvolatile memory cell. The cell includes: at least one first control region in the first well; conduction regions in the second well; and a floating gate region, which extends over portions of the first well and of the second well, is capacitively coupled to the first control region and forms a floating-gate memory transistor with the conduction regions. The insulating structure includes: first insulating regions, which separate the floating gate region from the first control region and from the second well outside the conduction regions and have a first thickness; and second insulating regions, which separate the floating gate region from the first well outside the first control region and have a second thickness greater than the first thickness.