  By means of near-simultaneous multi-wavelength VLBA measurements, we
determine for the first time the intrinsic size of Sgr A* to be 3.6 AU by <1 AU
with the major axis oriented essentially north-south. Contrary to previous
expectation that the intrinsic structure of Sgr A* is observable only at
wavelength shorter than 1 mm, we can discern the intrinsic source size at 7~mm
because (1) the scattering size along the minor axis is half that along the
major axis, and (2) the near simultaneous multi-wavelength mapping of Sgr A*
makes it possible to extrapolate precisely the minor axis scattering angle at
7~mm. The intrinsic size and shape place direct constraints on the various
theoretical models for Sgr A*.
