A method of fabricating a semiconductor device includes the steps of: depositing on a main surface of a semiconductor substrate a layer to be processed; depositing a base layer on the layer to be processed; depositing a first intermediate layer and then a second intermediate layer on the base layer; patterning the second intermediate layer while the base layer covers the layer to be processed; depositing a first mask pattern on the patterned second intermediate layer; patterning the second intermediate layer with the first mask pattern; patterning the first intermediate layer and the base layer with the patterned second intermediate layer to form a second mask pattern; and patterning the layer to be processed, with the second mask pattern.