A high voltage pulsed source was applied to gold thin films of 350 angstrom within an electrode gap of I turn. Films were deposited on alumina substrates with controlled surface micro-morphologies. Surface morphology parameters were determined by non-contact optical measurements and correlated with the electric field for surface breakdown at atmospheric pressure under air. The electric field required for the discharge to occur is much less than for a similar air gap under the same atmosphere pressure. The electric field increases with the decrease of peak height on surface, since the number and shape of microscopic sites for surface ionization greatly influence the breakdown process. The reliability of films against breakdown was characterized by Weibull statistics with numerous samples. The typical m modulus increases significantly with surface roughness at the micrometric scale, indicating a greater reliability of films. This is attributed to the distribution of metal voids on the surface, which change the distribution of current density during breakdowns. (c) 2006 Elsevier B.V. All rights reserved.