Ultrashort laser pulses deliver electromagnetic energy to matter causing its localized heating that can be used for both material removal via ablation/evaporation and driving interface chemical reactions. Here, it is shown that both mentioned processes can be simultaneously combined within straightforward laser nanotexturing of Si wafer in a functionalizing solution to produce a practically relevant metal–semiconductor surface nano-morphology. Such unique hybrid morphology represents deep-subwavelength Si laser-induced periodic surface structures (LIPSSs) with an extremely short period down to 70 nm and high-aspect-ratio nano-trenches loaded with controllable amount of plasmonic nanoparticles formed via laser-induced decomposition of the precursor noble-metal salts. Moreover, heat localization driving reduction process is utilized to produce surface morphology locally decorated with dissimilar plasmon-active nanoparticles. Light-absorbing deep-subwavelength Si LIPSSs loaded with controllable amount of noble-metal nanoparticles represent an attractive architecture for plasmon-related applications such as optical nanosensing where efficient coupling of the propagating optical waves to highly localized electromagnetic “hot spots” is a mandatory requirement. To support this statement, applicability of such hybrid morphology for fluorescence-based detection of nanomolar concentrations of mercury cations in solution is demonstrated.