  We discuss the hierarchy of Yukawa couplings in a supersymmetric three family
Standard-like string Model. The model is constructed by compactifying Type IIA
string theory on a Z_2 x Z_2 orientifold in which the Standard Model matter
fields arise from intersecting D6-branes. When lifted to M theory, the model
amounts to compactification of M-theory on a G_2 manifold. While the actual
fermion masses depend on the vacuum expectation values of the multiple Higgs
fields in the model, we calculate the leading worldsheet instanton
contributions to the Yukawa couplings and examine the implications of the
Yukawa hierarchy.
