Abstract: Provided is a method for simulating a semiconductor device. The method includes extracting a Hamiltonian and an overlap matrix of a semiconductor device using a density functional theory or a tight-binding method, calculating each of Bloch states for each corresponding energy, obtaining a first reduced Hamiltonian and a first reduced overlap matrix with a reduced matrix size, and calculating a final transformation matrix and a final energy band structure in which all of unphysical branches, wherein the semiconductor device includes a source region, a drain region, and a channel region between the source region and the drain region, wherein the channel region includes unit cells, each of which includes different material or has different structure.