A method of fabricating a semiconductor device includes designing a layout, performing an optical proximity correction (OPC) process to correct the designed layout, fabricating a first photomask using the corrected designed layout, and forming patterns on a substrate using the first photomask. The OPC process includes generating an OPC model and correcting the designed layout using the generated OPC model. The generation of the OPC model includes rasterizing a planar image of an actual pattern to obtain first label data, rasterizing a simulation image of a simulation pattern to obtain second label data, the simulation pattern being obtained using the OPC model, in which a parameter set including process parameters is set, comparing the first label data with the second label data to obtain comparison data, and correcting the process parameters of the parameter set, based on the comparison data.