Abstract: This invention relates to a method for fabrication of MOS transistors having LDD(Lightly Doped Drain) structure which comprises the steps of forming a gate insulation film on a semiconductor substrate of a first conduction type, forming a conduction layer for forming a gate pole on the gate insulation film, forming an oxidation prevention layer on the conduction layer, carrying out selective etchings of the oxidation prevention layer and the conduction layer to a certain thicknesses of areas except the gate pole area, forming an oxide film by an oxidation of the exposed portion of the conduction layer, carrying out a selective etching of the oxide film by using the oxidation prevention layer as a mask, forming a high density impurity area of a second conduction type in a predetermined area of the semiconductor substrate by a high density ion injection of the second conduction type impurity, removing the oxidation prevention layer and the oxide film, forming a low density impurity area of the second conduction