The low energy Si-2(-), Si-3(-) and Si-4(-) secondary ion signals resulting from Cs+ impact on Si appear to scale with the Cs uptake noted over the SIMS transient region in a manner consistent with the electron tunneling model. These populations, particularly Si-3(-) and Si-4(-) also exhibit a relative insensitivity to the presence of O (shown once sputter rate variations are accounted for). Profiles that more closely match the expected Si concentration gradient from a native oxide terminated Si wafer present within the SIMS transient region can also be obtained by simply dividing the Si-3(-) or Si-4(-) secondary ion intensities by the Si-2(-) intensities. This suggests a possible alternative route for reducing transient effects present in the negative secondary ion populations from Si wafers. Published by Elsevier B.V.