  We discuss both classical and semiclassical properties of extremal black
holes in theories where the dilaton and a modulus field are present. We find
that the corresponding 2-dim geometry is asymptotically anti-de Sitter rather
then asymptotically flat as in the purely dilatonic case. This fact has many
important consequences, which we analyze at length, both for the classical
behaviour and for the thermodynamical properties of the black hole. We also
study the Hawking evaporation process in the semiclassical approximation. The
calculations strongly indicates the emergence of a stable ground state as the
end point of the process. Some comments are made about the relevance of our
results for the problem of information loss in black hole physics.
