disclosed is a structure of a semiconductor device in which an internal circuit including a memory device and a transistor having an ldd structure and an input protection device for protecting the internal circuit are formed on one semiconductor substrate , and a method of manufacturing such a semiconductor device . the input protection device and the memory device are formed at the same time . the input protection device as well as the memory device includes source / drain regions formed of high concentration inpurity regions and formed in the surface of the semiconductor substrate , and a gate electrode formed of a plurality of conductor films and formed on the surface of the semiconductor substrate between the source / drain regions . when an abnormal voltage is applied to an interconnection for supplying an electrical signal to the internal circuit , a charge flows from the interconnection through one source / drain region of the input protection device into the semiconductor substrate , so that the internal circuit is protected against an excessive charge .