A semiconductor device fabrication method includes providing a layout; performing an optical proximity correction on the layout to generate a corrected layout; and forming a photoresist pattern on a substrate by using a photomask fabricated with the corrected layout. The OPC may include: extracting edges of a pattern, the edges including a first edge and a second edge that converge to define a corner; generating a thin mask image by applying a thin mask approximation to the pattern; changing the first edge and the second edge into a first stepped edge and a second stepped edge; and applying a three-dimensional filter to the first and second stepped edges to generate an optical image including the corrected layout of the pattern to which the 3D filter is applied from the thin mask image.