Simple galvanic reactions between highly doped n-type GaAs wafers and a pure aqueous solution of AgNO3 at room temperature provide an easy and efficient protocol to directly deposit uniform Ag nanoplates with tunable dimensions on the GaAs substrates. The anisotropic growth of the Ag nanoplates in the absence of surfactant molecules might be partially ascribed to the codeposition of oxides of gallium and arsenic, which are revealed by extensive data from electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, during the growth of the Ag nanoplates. The electron microscopic characterization shows that each Ag nanoplate has a "necked" geometry, that is, it pins on the GaAs lattices through only a tiny neck (with sizes of < 10 nm). In addition, the as-grown Ag nanoplates exhibit strong enhancement toward Raman scattering of materials on (or around) their surfaces.