A semiconductor device includes first and second voltage device regions and a deep well common to the first and second voltage device regions. An operation voltage of electronic devices in the second voltage device region is higher than that of electronic devices in the first voltage device region. The deep well has a first conductivity type. The first voltage device region includes a first well having the second conductivity type and a second well having the first conductivity type. The second voltage region includes a third well having a second conductivity type and a fourth well having the first conductivity type. A second deep well having the second conductivity type is formed below the fourth well. The first, second and third wells are in contact with the first deep well, and the fourth well is separated by the second deep well from the first deep well.