We quantize the spherically symmetric sector of generic charged black holes. Thermal properties are incorporated by
imposing periodicity in Euclidean time, with period equal to the inverse Hawking temperature of the black hole. This leads to an
exact quantization of the area (A) and charge (Q) operators. For the Reissner–Nordström black hole, A = 4πG¯h(2n + p + 1)
and Q= me, for integers n,p,m. Consistency requires the fine structure constant to be quantized: e2/¯h = p/m2. Remarkably,
vacuum fluctuations exclude extremal black holes from the spectrum, while near extremal black holes are highly quantum
objects. We also prove that horizon area is an adiabatic invariant.