  We show that the cosmological constant may be reduced by thermal production
of membranes by the cosmological horizon, analogous to a particle ``going over
the top of the potential barrier", rather than tunneling through it. The
membranes are endowed with charge associated with the gauge invariance of an
antisymmetric gauge potential. In this new process, the membrane collapses into
a black hole, thus the net effect is to produce black holes out of the vacuum
energy associated with the cosmological constant. We study here the
corresponding Euclidean configurations ("thermalons"), and calculate the
probability for the process in the leading semiclassical approximation.
