US Patent 9831232 ESD protection device

An electrostatic protection includes a buried layer having an outer region and an inner region which are heavily doped regions of a first conductivity type. The inner region is surrounded by an undoped or lightly doped ring region. The ring region is surrounded by the outer region. The device further includes a semiconductor region over the buried layer, a first well of the first conductivity type in the semiconductor region, a first transistor in the semiconductor region, and a second transistor in the semiconductor region. The first well forms a collector of the first transistor and a collector of the second transistor.