We report on the optical and electrical properties of MgZnO/Ag/MgZnO (MAM) grid electrodes grown at room temperature; these are proposed as an alternative to metal-based grid electrodes to meet the requirement for high stability in a harsh environment. The optical transmittance of Ag grid electrodes improved when the Ag grid layer was embedded in an MgZnO grid layer regardless of the fill factor. This improvement depends critically on the Ag grid layer thickness in the MAM grid electrodes. The Haack figure of merit for a MAM grid electrode with a 20 nm-thick Ag grid layer was approximately threefold higher than that of an Ag grid electrode. The electrode has an average transmittance of 85.8% at wavelengths range from 400 to 1100 nm and a sheet resistance of 26.9 omega/sq. These results indicate that MAM grid electrodes can be an alternative to metal-based grid electrodes in optoelectronic devices that require stable wideband operation in a harsh environment and over a wide wavelength region.