A low-field mobility model for square GAA MOSFETs has been developed. The model is analytical and explicit, so it can be used in device simulators and, most importantly, in compact models of these Multi-gate devices for circuit simulation purposes. We have made use of a simulator that includes quantum effects to characterize the electron mobility of square GAA MOSFETs with different sizes for the usual gate voltages and operation regimes. The dependencies with the silicon core lateral size, the inversion charge and the surface roughness are included. The phonon, surface roughness and Coulomb mobility components are modeled separately by means of the Matthiessen rule. Finally, we have performed a comparison between our model and experimental results for validation purposes. We find that the experimental results are well reproduced by our model. (C) 2013 Elsevier Ltd. All rights reserved.