The present invention provides a method for manufacturing contact holes of a semiconductor device, including a first dielectric layer is provided, a first region and a second region are defined on the first dielectric layer respectively, at least two cutting hard masks are formed and disposed within the first region and the second region respectively, at least two step-height portions disposed right under the cutting hard masks respectively. Afterwards, at least one first slot opening within the first region is formed, where the first slot opening partially overlaps the cutting hard mask and directly contacts the cutting hard mask, and at least one second contact opening is formed within the second region, where the second contact opening does not contact the cutting hard mask directly, and at least two contact holes are formed, where each contact hole penetrates through each step height portion.