Abstract. - An overall three-dimensional photolithography simulator is presented, which has been developed for workstation based application. The simulator consists of three modules according to the fundamental processes of photolithography, namely imaging, exposure/bleaching and development. General illumination forms are taken into account. The nonlinear bleaching reaction of the photoresist is considered and electromagnetic light-scattering due to a nonplanar topography is treated by solving repeatedly the Maxwell equations within an inhomogeneous medium. A novel extension of the two-dimensional differential method into the third dimension is presented and a numerically efficient implementation for exposure simulation under partial coherent illumination is described. The development process is simulated with a cellular based surface advancement algorithm.