A manufacturing method for forming a semiconductor device includes: first, a substrate is provided, a fin structure is formed on the substrate, and a plurality of gate structures are formed on the fin structure, next, a hard mask layer and a first photoresist layer are formed on the fin structure, an first etching process is then performed on the first photoresist layer, afterwards, a plurality of patterned photoresist layers are formed on the remaining first photoresist layer and the remaining hard mask layer, where each patterned photoresist layer is disposed right above each gate structure, and the width of each patterned photoresist is larger than the width of each gate structure, and the patterned photoresist layer is used as a hard mask to perform an second etching process to form a plurality of second trenches.