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Abstract

A body of semiconductor material for use in forming a low voltage surface breakdown protection device comprises a substrate having upper and lower surfaces, and a PN junction formed between first (16) and second (14) regions of the body in which in the intended operation of the device reverse breakdown of the junction occurs. The substrate forms the first region (16) which is of lower impurity concentration than the second region (14) and the second (14) region extends to the upper surface of the substrate (16). First and second edge breakdown regions (42, 44) extending to the upper surface of the substrate are provided in the first region (16). They are of the same conductivity type as and of higher impurity concentration than the first region (16). An insulating layer (46) is formed on the upper surface of the substrate over the junction between the second edge breakdown region (26) and the second region (14) for protecting the interface between the insulating layer (46) and the edge breakdown region (26) during subsequent processing. The insulating layer (46) has a low concentration of impurities thereby to restrict current flow adjacent the interface between the insulating layer (46) and the edge breakdown region (26).

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