Disclosed is a method for simulating characteristics of a semiconductor device. An overlap matrix and a Hamiltonian representing atomic interaction energy information of a target semiconductor device are extracted by using a density functional theory (DFT), and Bloch states for corresponding energies are calculated based on the Hamiltonian, the overlap matrix, and energy-k relation within an effective energy region. A first reduced Hamiltonian and a first reduced overlap matrix having a reduced matrix size are obtained by applying the Hamiltonian and the overlap matrix to a transformation matrix that is obtained by orthonormalizing a matrix representing the Bloch states. A final transformation matrix and a final energy band structure where all unphysical branches, which are energy bands not corresponding to a first energy band structure in a second energy band structure, are removed within the effective energy region are calculated.