Matrix model for Dirichlet open string

We discuss the open string ending on D p-branes in IKKT framework. First we determine the boundary conditions of Green-Schwarz superstring which are consistent with supersymmetry and κ-symmetry. We point out some subtleties arising from taking the Schild gauge and show that in this gauge the system incorporates the limited dimensional D p-branes (p=3,7). The matrix regularization for the Dirichlet open string is given by gauge group SO(N). When p=3, the matrix model becomes the dimensional reduction of a 6 dimensional N=1 super Yang-Mills theory.