A bidirectional switch formed in a substrate includes first and second main vertical thyristors in antiparallel connection. A third auxiliary vertical thyristor has a rear surface layer in common with the rear surface layer of the first thyristor. A peripheral region surrounds the thyristors and connects the rear surface layer to a layer of the same conductivity type of the third thyristor located on the other side of the substrate. A metallization connects the rear surfaces of the first and second thyristors. An insulating structure is located between the rear surface layer of the third thyristor and the metallization. The insulating structure extends under the periphery of the first thyristor. The insulating structure includes a region made of an insulating material and a complementary region made of a semiconductor material.