Abstract: A surge arrester of modular form, including a metal oxide varistor disk having a coaxial shunt gap located within the disk. The metal oxide varistor disk has a hole located essentially through the center of the disk and includes top and bottom electrode plates having centrally located projections which protrude inwardly of the disk into the hole of the disk, thereby forming a shunt gap within the disk. The module may be used unhoused in under-oil applications or as a component part of a housed arrester. For under-oil applications, the electrode plates are solder sealed to the disk providing a seal preventing oil or moisture from entering the hole in the shunt gap. As an alternate embodiment the surge arrester module may include a series of two or more of such disks stacked between the top and bottom electrode plates.