  In the heavy quark limit a heavy baryon which contains two heavy quarks is
believed to be composed of a heavy diquark and a light quark. Based on this
picture, we evaluate the weak semileptonic decay rates of such baryons. The
transition form factors between two heavy baryons are associated with those
between two heavy mesons by applying the superflavor symmetry. The effective
vertices of the W-boson and two heavy diquarks are obtained in terms of the
Bethe-Salpeter equation. Numerical predictions on these semileptonic decay
widths are presented and they will be tested in the future experiments.
