A semiconductor device and fabrication method thereof are provided. The fabrication method include: providing a to-be-etched material layer; forming a plurality of discrete sacrificial layers on the to-be-etched material layer; forming first initial spacers on sidewalls of each sacrificial layer, where each first initial spacer includes a first bottom region and a first top region on the first bottom region; removing the sacrificial layers; removing the first bottom region of the first initial spacer to form a first spacer from the first top region; forming second spacers on sidewalls of each first spacer; removing the first spacer; and etching the to-be-etched material layer by using the second spacers as an etch mask.