  We study the entropy of the Gibbons-Maeda-Garfinkle-Horowitz-Strominger
(GMGHS) charged black hole, originated from the effective action that emerges
in the low-energy of string theory, beyond semiclassical approximations.
Applying the properties of exact differentials for three variables to the first
law thermodynamics we derive the quantum corrections to the entropy of the
black hole. The leading (logarithmic) and non leading corrections to the area
law are obtained.
