  We present an angle-resolved photoemission study of a ternary phase change
material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable
cubic phase. The observed upper bulk valence band shows a minimum at Gamma-bar
being 0.3 eV below the Fermi level E_F and a circular Fermi contour around
Gamma-bar with a dispersing diameter of 0.27-0.36 Anstroms^-1. This is in
agreement with density functional theory calculations of the Petrov stacking
sequence in the cubic phase which exhibits a topological surface state. The
topologically trivial cubic KH stacking shows a valence band maximum at Gamma
in line with all previous calculations of the hexagonal stable phase exhibiting
the valence band maximum at Gamma for a trivial Z_2 topological invariant nu_0
and away from Gamma for non-trivial nu_0. Scanning tunneling spectroscopy
exhibits a band gap of 0.4 eV around E_F.
