Using adiabatic invariance and the Bohr-Sommerfeld quantization rule we
investigate the entropy spectroscopy of a charged black hole of heterotic
string theory. It is shown that the entropy spectrum is equally spaced
identically to the Schwarzschild, Reissner-Nordstr\"om and Kerr black holes.
Since the adiabatic invariance method does not use quasinormal mode analysis,
there is no need to impose the small charge limit and no confusion on whether
the real part or imaginary part is responsible for the entropy spectrum.Comment: 8 pages, no figure