The microstructures of amorphous solid-core carbon nanofibers (CNFs) synthesized in flames show long-range disorder, which makes it difficult to reconstruct their three-dimensional atom configurations by popular characterization methods. Using a reverse Monte Carlo method, the atom configurations of CNFs were derived from X-ray diffraction data, and these were used to calculate the Fermi levels, density of electronic states and electrical conductivity of the CNFs. The calculated electronic structures of CNFs indicate that the amorphous CNFs are semiconducting. Experimentally, the I-V curve of the CNFs was investigated and shown to be symmetrical and nonlinear, indicating the semiconductivity of the CNFs, which is good agreement with calculated results.