Electronic structure calculations are presented for various model structures of the crystalline and amorphous phases of Ge2Sb2Te5. The structures are all found to possess a band gap of order 0.5 eV, indicating closed shell behaviour. It is pointed out that structural vacancies in A7-like Ge2Sb2Te5 are not electronically active. In addition, A7-like structures do not support valence alternation pair defects, which are one model of the conduction processes in the amorphous phase in non-volatile memories. (c) 2007 Elsevier B.V. All rights reserved.