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In the context of type-ⅡA orientifold compactifications,we discuss the fermion masses in a two-singlet-extended minimal-supersymmetric-standard-model four-stack quiver with U(3) × Sp(1) × U(1) × U(1) gauge symmetry.The corresponding effective superpotential exhibits hierarchical coupling term scales giving a partial solution to the fermion masses problem.Using the known data with upper bound neutrino masses mvτ ＜～ 2 eV,we estimate the relevant scales for the model.It has been shown that important particle physics can be realized in type-Ⅱ superstring models by using the mechanism of intersecting D-branes in orientifold compactifications.[1-6] In such compactifications,the gauge groups arise from stacks of D-branes that fill four-dimensional spacetime and wrap the three-cycles in the inteal Calabi-Yau threefold.However,matter fields arise at the intersection of two different D-brane stacks in inteal space and their multiplicity is given by the topological intersection numbers of the respective three-cycles.Their interactions are subject to restrictions of additional global U(1)s exhibited by orientifold compactifications.[7-10] Stringy effects have a crucial role in this regard,as they give corrections to the superpotential by inducing the missing couplings relevant for fermion masses.This method provides an acceptable effective low energy description reproducing the standard model or some extensions.[11,12]