A correlation of SIMS ion intensities to the molecular weight of linear, trimethyl‐terminated polydimethyl siloxane (PDMS) has been developed by normalizing PDMS endgroup‐related signal to backbone‐related signal for a set of well‐characterized polymers with narrow molecular weight distributions. These initial experiments on thick PDMS films illustrate that PDMS molecular weight can be estimated using SIMS. A second paper describes the challenges in analyzing thin PDMS films on metal and polymer substrates. PDMS molecular weight determination is important to understanding surface‐related performance of materials using silicone additives across many different platforms including coefficient of friction, slip, mar, mold release, and nonstick properties as well as providing more specific characterization of surface contamination.