We show that the leading order solution describing an extremal electrically charged black hole in string theory is, in fact, an exact solution to all orders in ${\alpha }^{\prime }$ when interpreted in a Kaluza-Klein fashion. This follows from the observation that it can be obtained via dimensional reduction from a five-dimensional background which is proved to be an exact string solution.

• Received 11 August 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.3351