may be non isolated having a common terminal connected to the substrate or isolated from the substrate it may comprise any of several possible esd clamp devices including a ggnmos as shown in fig4 a an npn esd clamp as shown in fig4 b and 4d an esd clamp diode as shown in fig4 c or other related devices top esd clamp 401 is isolated from the substrate such that it can float to a high voltage and thus be stacked in series with bottom esd clamp 402 top esd clamp 401 may comprise any of several possible esd clamp devices including a ggnmos as shown in fig4 a an npn esd clamp as shown in fig4 b an esd clamp diode as shown in fig4 c and 4d or other related devices the top and bottom esd clamp devices may the same type or different types of devices may be used for the top and bottom clamps respectively for example an npn esd clamp may be used on the bottom and an isolated esd clamp diode on the top as shown in stacked esd clamp structure 400 d in fig4 d fig5 shows a cross sectional view of an isolated npn esd clamp 500 an n collector 503 is separated from n emitters 504 a and 504 b by a significant distance for example 10 100 um to provide some ballasting resistance to distribute the esd current uniformly p base contacts 505 a and 505 b are spaced from the.