SEMICLASSICAL EXTREMAL BLACK-HOLES

Extremal black holes are studied in a two-dimensional model motivated by a dimensional reduction from four dimensions. Their quantum-correct ed geometry is calculated semiclassically and a mild singularity is sh own to appear at the horizon. Extensions of the geometry past the hori zon are not unique but there are continuations free from malevolent si ngularities. A few comments are made about the relevance of these resu lts to four dimensions and to the study of black hole entropy and info rmation loss.