  We associate to any irreducible germ S of complex quasi-ordinary hypersurface
an analytically invariant semigroup. We deduce a direct proof (without passing
through their embedded topological invariance) of the analytical invariance of
the normalized characteristic exponents. These exponents generalize the generic
Newton-Puiseux exponents of plane curves. Incidentally, we give a toric
description of the normalization morphism of the germ S.
