Systematic electronic transport measurements in nanometer-scale junctions containing self-assembled monolayers of alkyl molecules are reported using nanowell device structures. The comprehensive temperature-variable current-voltage characterizations and statistical analysis for the acquired transport data show that direct tunneling indeed can be assigned as the dominant charge transport mechanism of the alkyl monolayers in a voltage range 1 V. The intrinsic tunneling characteristics of alkyl molecular junctions are examined by excluding other parasitic conduction mechanisms by the data analyses and statistically defining representative data. The demonstrated intrinsic tunneling characteristics are well consistent with numerous previous reports for alkyl-based monolayers. The current characteristics are temperature independent and exponentially depend on the molecular length. The tunneling decay coefficient is determined as 0.83– 0.73 Å −1 in the bias range from 0.1 to 1.0 V and is independent of temperature. The statistical histogram of current densities for all direct tunneling devices exhibits log-normal distribution, which is likely due to a variation in tunneling distance. © 2008 American Vacuum Society.