1. (in a p-n-p bipolar junction transistor) A means for limiting channel formation by surrounding the n-type base entirely with a ring of highly doped low resistivity p-type material.

2. (in a MOS integrated circuit) A region of highly doped material of the same type as the lightly doped substrate. This increases the field threshold voltage and inhibits the formation of spurious field-effect transistors caused when interconnections pass between adjacent drain regions.