Dark currents in MNS capacitors are studied as a function of metal electrode material and insulator thickness. Dark currents sensitively reflect different electrode materials for thin (∼200 A˚) nitride films. Thus, it is found that high‐work‐function metals increase conduction under metal positive bias by enhanced hole injection and low‐work‐function metals increase conduction under metal negative bias by enhanced electron injection. Similar polarity differences are observed betwenn‐type andp‐type degenerate Si substrates. These contact differences disappear as the nitride becomes thicker and the thickness of trapped space‐charge layers near the contacts becomes small compared to the nitride thickness.