We demonstrate the all-solution-based fabrication of metal-nanodot-decorated semiconductor nanorod structures, with the entire process performable at very low or room temperatures. On the surfaces of semiconducting ZnO nanorods (ZNRs) hydrothermally grown on a solution-processed Ag layer at 90 °C, Ag nanodots are reduced from Ag cations in an ionic solution at room temperature by taking UV-induced electrons from ZNRs. Ag nanodots can be deposited at a specific position (top, bottom, or whole region) of the ZNRs by using a controlled ionic Ag solution coating method. We investigate the UV-assisted room-temperature photoreduction (RTPR) mechanism by focusing on the roles of ZnO and solvent. We further examine that the size, density, and spatial distribution of Ag nanodots can be controlled by regulating the concentration of the ionic Ag solution and RTPR time. The resulting hybrid Ag/ZNR architecture, processable on a large-area flexible substrate, exhibits significantly enhanced photocurrent level, responsivity, and selectivity for the incident UV light due to the localized surface plasmon resonance of the Ag nanodots and rapid electron transfer across the Ag/ZnO interface. Our all-solution-based room-temperature approach offers an environmentally sustainable, low-cost, and scalable method for the design and fabrication of metal-nanodot-decorated semiconductor nanostructures applicable to optoelectronic transducers and many other applications.