In the present work, we report the one-step synthesis of AgxCu100-x bimetallic nanoparticles (NPs) on p-type silicon (p-Si) supports and their application as photocathodes for the photoelectrochemical CO2 reduction reaction (PEC-CO2RR). Based on the metalassisted chemical etching (MACE) of Si in HF medium, the proposed method allows the formation of NPs homogeneously distributed on the Si surface, with an excellent control of their bimetallic composition, surface coverage and morphology by adjusting the experimental conditions (deposition time, precursor concentrations). Microstructural studies reveal a phaseseparated polycrystalline structure for the bimetallic with a high dispersion of Ag and Cu nanocrystallites, remarkable for Ag/Cu nanostructures synthesized by soft chemistry. The analysis of the PEC-CO2RR shows a better performance of Ag50Cu50/p-Si than Ag/p-Si and Cu/p-Si, with an onset potential shift of 840 mV and a ratiometric power saved of ~3% compared to an analogous metal electrode in CO2 saturated 0.5 M NaHCO3. Photoelectrolysis tests under 1 sun illumination coupled with gas chromatography demonstrate the capacity of the bimetallic photocathode to guide the selectivity with the applied potential. Thus, CO2 conversion to CO and CH4 are achieved on Ag50Cu50/p-Si, with a maximum Faradaic efficiency (FE) of 26 % and 18.2% at-0.72 and-0.87 VRHE, respectively.