An experimental and theoretical investigation of the temperature dependence of the dc conductivity in heavily ar-senic-doped polycrystalline silicon thin films is presented. Measured results indicate that the carrier trapping model which is traditionally used to describe polysilicon transport fails in the heavy doping regime. After consideration of alternative models, the electrical nature of the grain boundary is found to be best described as a conduction process with two different activation energies. Reasonable agreement with data is obtained when the grain and grain boundary conductivities are combined using a model of the film microstructure. Nonuniform grain size and distributions are considered. © 1989, The Electrochemical Society, Inc. All rights reserved.