PURPOSE: To enhance the density of a semiconductor device by constructing the side of a separating groove so that silicon nitride films are contacted and a contact window is extended from a diffused layer to eliminate a shortcircuit between the diffused layer and a substrate by metal wirings.

CONSTITUTION: Grooves 3, 3' are formed on the main surface of a P-type semiconductor substrate 1 approx. 2μ of depth with an oxide film 2 as a mask, the surfaces of the substrate in the grooves 3, 3' are nitrided in high temperature atmosphere including ammonium to grow several hundreds Angstroms of a thermal nitride films 4, separating oxides 5 are then deposited in the grooves 3, 3', etched and buried. Subsequently, a gate insulating film 5 and a gate 7 are formed, N-type diffused layers 8, 8' are formed as a source and a drain by an ion implanting method, the entirety is covered with an insulating film 9 which mainly contains an oxide film, and a contact window 10 is formed by etching through the film 9. At this time, the window 10 is extended from the layer 8. Then, metal wirings 11 made of aluminum are formed to form a contact with the layer 8 in the portion 10a of the window 10.