ELECTRICAL SURGE PROTECTIVE APPARATUS

1 . An electrical surge protective apparatus comprising:

a base region containing impurities of a first conductivity type;

a first semiconductor region joined to said base region on an upper surface side thereof and containing impurities of a second conductivity type that is different from said first conductivity type;

a second semiconductor region joined to said base region on a lower surface side thereof and containing impurities of a same conductivity type as that of said second conductivity type;

a high resistance region electrically connected to both said base region and said second semiconductor region, said high resistance region containing impurities of a same conductivity type as that of said second conductivity type and having a lower impurity concentration than said second semiconductor region;

a first electrode terminal electrically connected to said first semiconductor region; and

a second electrode terminal electrically connected to said second semiconductor region.

2 . The electrical surge protective apparatus according to claim 1 , wherein said high resistance region is electrically connected to all of said base region, said second semiconductor region and said first semiconductor region.

3 . The electrical surge protective apparatus according to claim 1 , wherein said first semiconductor region, said base region and said second semiconductor region are connected in series thereby to have a bipolar transistor structure.

4 . The electrical surge protective apparatus according to claim 3 , wherein:

said first semiconductor region, said base region and said second semiconductor region in this order are formed within a semiconductor substrate in a depth direction of said semiconductor substrate;

said first semiconductor region is formed so as to be surrounded by a part of said base region in the vicinity of a main surface of said semiconductor substrate;

said part of said base region surrounding said first semiconductor region is formed so as to be surrounded by a part of said second semiconductor region in the vicinity of the main surface of said semiconductor substrate; and

said high resistance region is joined to said part of said base region and formed between said first semiconductor region and said second semiconductor region.

5 . The electrical surge protective apparatus according to claim 3 , further comprising a semiconductor substrate disposed between said second electrode terminal and said second semiconductor region, and containing impurities of a same conductivity type as that of said second conductivity type,

wherein said second semiconductor region is formed within an epitaxial layer that is epitaxially grown on said semiconductor substrate.

6 . The electrical surge protective apparatus according to claim 5 , wherein:

said first semiconductor region, said base region and said second semiconductor region in this order are formed within said epitaxial layer in a depth direction of said epitaxial layer;

said first semiconductor region is formed so as to be surrounded by a part of said base region in the vicinity of a main surface of said epitaxial layer;

said part of said base region is formed so as to be surrounded by a part of said second semiconductor region in the vicinity of the main surface of said epitaxial layer; and

said high resistance region is joined to said part of said base region in the vicinity of the main surface of said epitaxial layer, and formed between said first semiconductor region and said second semiconductor region.