  We investigate phenomenologically viable four- and five-stack MSSM D-brane
quivers which exhibit realistic fermion mass hierarchies. In our analysis, the
mass hierarchies arise either from higher order terms containing the VEV's of
SM singlets or from D-instanton effects, where the latter utilizes either
family splitting or a factorizable Yukawa matrix. Extending the systematic
bottom-up analysis of arXiv:0905.3379, we present the only four-stack quiver
with a semi-realistic Yukawa texture. Investigation of five-stack MSSM models
reveals many more quivers with analogous Yukawa textures, as well as a few
examples which exhibit three different mass scales for the up-quarks,
down-quarks, and electrons. Potential problems in this class of quivers are the
presence of U(1) instantons, which might lead to undesired effects, such as
R-parity violating couplings, and the presence of dimension 5 operators that
could lead to rapid proton decay. We present a five-stack setup which overcomes
all of these problems and exhibits three different mass scales for the
up-quarks, down-quarks and electrons.
