A layout modification method for fabricating a semiconductor device is provided. The layout modification method includes calculating uniformity of critical dimensions of first and second portions in a patterned layer by using a layout for an exposure manufacturing process to produce the semiconductor device. A width of the first and second portions equals a penumbra size of the exposure manufacturing process. The penumbra size is utilized to indicate which area of the patterned layer is affected by light leakage exposure from another exposure manufacturing process. The layout modification method further includes compensating non-uniformity of the first and second portions of the patterned layer according to the uniformity of critical dimensions to generate a modified layout. The first portion is divided into a plurality of first sub-portions. The second portion is divided into a plurality of second sub-portions. Each second sub-portion is surrounded by two of the first sub-portions.