  The global stability of R-charged AdS black holes in a grand canonical
ensemble is examined by eliminating the constraints from the action, but
without solving the equations of motion, thereby constructing the reduced
action of the system. The metastability of the system is found to set in at a
critical value of the chemical potential which is conjugate to the R-charge.
The relation among the small black hole, large black hole and the instability
is discussed. The result is consistent with the metastability found in the
AdS/CFT-conjectured dual field theory. The "renormalized" temperature of AdS
black holes, which has been rather ad hoc, is suggested to be the boundary
temperature in the sense of AdS/CFT correspondence. As a byproduct of the
analysis, we find a more general solution of the theory and its properties are
briefly discussed.
