  We study the recently discovered Theta^+ baryon in the context of the
perturbative chiral quark model. The basic configuration of the Theta^+ is set
up as a pentaquark bound state, where the single particle wave functions are
the ground state solutions of a confining potential. We classify the resulting
pentaquark multiplets as the J^P=1/2^- and 3/2^- flavor SU(3) antidecuplet. The
full mass spectrum of the multiplets is determined by including meson and gluon
cloud contributions inducing flavor SU(3) breaking. Mainly due to the
semi-perturbative gluon effects the resulting 3/2^- antidecuplet is about 185
MeV heavier than the 1/2^- one. We assign the observed Theta^+ baryon as a
member of the 1/2^- antidecuplet and discuss in particular the relation to the
recent experimental signal for a Xi^{--} baryon.
