Abstract: A method of fabricating a metal oxide semiconductor transistor comprising:a silicon substrate having a first conductivity type in which its central portion having a channel region has a recessed surface and other portion excepting the central portion has a flattened surface, a thin gate oxide film formed on the recessed surface of the silicon substrate, an oxide film formed on the flattened of the silicon substrate and having a thickness a little thicker than that of the gate oxide film, a gate formed on the gate oxide film and having a structure in which its upper surface is flattened and its lower surface is convex, a thick cap oxide film on the gate, a low concentration source region and drain region having a second conductivity type overlapped completely with the gate and formed on a portion adjacent to the channel region of the recessed surface of the silicon substrate, a high concentration source region and drain region having the second conductivity type formed on the flattened surface of the silicon s