A MOSFET comprising a gate oxide layer on a silicon substrate, a polysilicon gate formed on the gate oxide layer, the length of which gradually widens going from bottom to top, a side gate oxide layer formed by an oxidation process surrounding the polysilicon gate, the side gate oxide layer also gradually widening from bottom to top, a source/drain region beside the gate oxide layer, a connection element having a stacked structure of a polysilicon and/or polycide layer on the field oxide, a doped polysilicon side wall beside the side gate oxide layer and making electric connection between the source/drain region and the connection element.