A device is described comprising a substrate of a first conductivity type having a first dopant concentration, a first well formed in the substrate, a second well of the first conductivity type formed in the substrate and being deeper than the first well, the second well having a higher dopant concentration than the first dopant concentration, and a nonvolatile memory cell formed on the second well. A device is described comprising four wells of various conductivity types with a nonvolatile memory cell formed on the second well. A device is described comprising a plurality of wells for isolating transistors of a plurality of voltage ranges, wherein each one of the plurality of wells contains at least one transistor of a particular voltage range, and wherein transistors of only one of the plurality of voltage ranges are within each of the plurality of wells. A method is described of isolating transistors of a first voltage range from transistors of another voltage range, comprising forming a first well to hold transistors only of a first particular voltage range, and forming a second well to hold transistors only of a second particular voltage range.