Method of electrically isolating individual semiconductor circuits in a wafer

In a method of electrically isolating individual semiconductor circuits in a wafer having a plurality of said semiconductor circuits formed therein, said wafer being of the type having first and second layers of a first conductivity type separated by an intervening third layer of a second conductivity type, said transistor circuits to be separated from each other and from the wafer into individual semiconductor chips by severing the wafer along intersecting boundary lines defining the boundaries of individual semiconductor circuit chips, the steps of:

• forming a lateral isolation region of first conductivity type passing through the third layer and extending along the boundary line between individual semiconductor circuit chip portions so as to form a buried P-N junction between said lateral isolation region and the third layer between the third layer and each of the first and second layers along the individual chip boundary lines, whereby undesired leakage current between individual ones of the semiconductor circuits is prevented in the wafer to permit probe testing of the individual semiconductor chips prior to separating the individual circuit chips from the wafer.