A semiconductor device includes a memory transistor (10A) which is capable of being irreversibly changed from a semiconductor state where drain current Ids depends on gate voltage Vg to a resistor state where drain current Ids does not depend on gate voltage Vg. The memory transistor (10A) includes a gate electrode (3), a metal oxide layer (7), a gate insulating film (5), and source and drain electrodes. The drain electrode (9d) has a multilayer structure which includes a first drain metal layer (9d1) and a second drain metal layer (9d2), the first drain metal layer (9d1) being made of a first metal whose melting point is not less than 1200° C., the second drain metal layer (9d2) being made of a second metal whose melting point is lower than that of the first metal. Part P of the drain electrode 9d extends over both the metal oxide layer (7) and the gate electrode (3) when viewed in a direction normal to a surface of the substrate. The part (P) of the drain electrode (9d) includes the first drain metal layer (9d1) and does not include the second drain metal layer (9d2).