  We suggest a short-living supermassive magnetar model to account for the
X-ray flares following short $\gamma-$ray bursts. In this model, the central
engine of the short $\gamma-$ray bursts is a supermassive millisecond magnetar.
The X-ray flares are powered by the dipole radiation of the magnetar. When the
magnetar has lost a significant part of its angular momentum, it collapses to a
black hole and the X-ray flares disappear abruptly. Two important predictions
of this model are (i) X-ray flares much more energetic than that detected in
GRB 050724 may be detectable in the coming months and years by the XRT onboard
{\it Swift}. (ii) The short GRBs with X-ray flares may occur outside of their
host galaxy.
