Semiconductor device having a protective circuit

摘要

A semiconductor device includes a protective circuit at an input/output port thereof, wherein the protective circuit includes a plurality of protective MOS transistors. A diffused region (10a) is disposed between the n-type source/drain regions (14n, 16n) and a guard ring (18n) formed in a p-well (11b) for encircling the source/drain regions (14n, 16n) of the protective transistors. The diffused region (10a) is of lightly doped p-type or of an n-type and increases the resistance of a parasitic bipolar transistor (12) formed in association with the protective transistors. The increase of the resistance assists protective function of the protective device against an ESD failure of the internal circuit of the semiconductor device.