  Current-voltage curves of small area hysteretic intrinsic Josephson
junctions, for which the Josephson energy $E_J=\hbar J_c/2e$ is of order of
thermal energy $kT$, are investigated. A non-monotonic temperature dependence
of the switching current is observed and explained by thermal phase
fluctuations. At low temperatures premature switching from the superconducting
into the resistive state is the most important effect of fluctuations. At high
temperatures only a single resistive branch is observed. At the cross-over
temperature a hysteretic phase-diffusion branch exists. It shows the importance
of a frequency-dependent impedance of an external circuit formed by the leads.
