  We analyze the perturbative stability of non-supersymmetric intersecting
brane world models on tori. Besides the dilaton tadpole, a dynamical
instability in the complex structure moduli space occurs at string disc level,
which drives the background geometry to a degenerate limit. We show that in
certain orbifold models this latter instability is absent as the relevant
moduli are frozen. We construct explicit examples of such orbifold intersecting
brane world models and discuss the phenomenological implications of a three
generation Standard Model which descends naturally from an SU(5) GUT theory. It
turns out that various phenomenological issues require the string scale to be
at least of the order of the GUT scale. As a major difference compared to the
Standard Model, some of the Yukawa couplings are excluded so that the standard
electroweak Higgs mechanism with a fundamental Higgs scalar is not realized in
this set-up.
