MOS TRANSISTOR

PURPOSE:To provide a MOS transistor which enables a threshold voltage to be controlled according to changes in a flat band voltage, by distributing specified metal elements ideally in an oxide film. CONSTITUTION:Chromium in concentration of over 1X10 /cm is contained only in an interface between a silicon oxide film 4 and its upper electrode 5 and in a silicon oxide film 4 in the vicinity of the interface, a region 6 containing chromium in that concentration has the silicon oxide film 4, thickness of which is under 75%, the concentration of impurities supplying holds or electrons into the upper electrode 5 is controlled under 1X10 /cm , and the concentration of impurities supplying holes or electrons into a silicon substrate 1 is controlled under 1X10 /cm . Consequently, a threshold voltage can be controlled according to changes in a flat band voltage with hardly deteriorating insulation of the silicon oxide film and having almost no adverse effects on electrical characteristics in the silicon substrate.