In this work, we have prepared Ag-doped Ge-Ga-Sb-S glasses by a solid-state electric field-assisted (EFA) diffusion method. It has been found that a large amount of silver metal can be introduced into the glass matrix. The distribution of silver has been measured by secondary ion mass spectrometry. Two models, i.e. the thin- and thick-film models based on the classic diffusion theory have been applied to fit the experimental data. We have found that the modeling depends strongly on the diffusion temperature, e.g., an acceptable fitting can be obtained only by the thick-film model in case of low diffusion temperature. The refractive index has increased significantly without the glass surface being contaminated after the diffusion. The solid-state EFA diffusion method is a very promising and effective way of making single-mode planar waveguides.