Abstract: An improved MNOS IGFET with stable long term memory retention, hysteresis and capable of LSI fabrication with reproducible electrical characteristics. The device comprises a field oxide adhered to a semiconductive substrate of a first conductivity type having a spaced pair of diffusion regions of opposite conductivity type separated by an interstitial layer of the substrate; a composite dielectric layer adhered to the oxide layer, the composite layer comprising a first dielectric layer adhered directly to the oxide layer and a second dielectric layer adhered to the first dielectric layer; and a conductive electrode adhered to the second dielectric layer.The first dielectric layer has a thickness in the range from about 20% to about 50% of the total thickness of the composite dielectric layer, and the electrical conductivity of the second dielectric layer is less than that of the first dielectric layer.