As crystalline semiconductor nanowires are thinned down to a single-unit-cell thickness, many fascinating properties could arise pointing to promising applications in various fields. A grand challenge is to be able to controllably synthesize such ultrathin nanowires. Herein, we report a strategy, which synergizes a soft template with oriented attachment (ST-OA), to prepare high-quality single-unit-cell semiconductor nanowires (SSNWs). Using this protocol, we are able to synthesize for the first time ZnS and ZnSe nanowires (NWs) with only a single-unit-cell thickness (less than 1.0 nm) and a cluster-like absorption feature (i.e., with a sharp, strong, and significantly blue-shifted absorption peak). Particularly, the growth mechanism and the single-unit-cell structure of the as-prepared ZnS SSNWs are firmly established by both experimental observations and theoretical calculations. Thanks to falling into the extreme quantum confinement regime, these NWs are found to only absorb the light with wavelengths shorter than 280 nm (i.e., solar-blind UV absorption). Utilizing such a unique property, self-powered photoelectrochemical-type photodetectors (PEC PDs) based on the ZnS SSNWs are successfully fabricated. The PDs after interface modification with TiO2 exhibit an excellent solar-blind UV photoresponse performance, with a typical on/off ratio of 6008, a detectivity of 1.5 X 10(12) Jones, and a responsivity of 33.7 mA/W. This work opens the door to synthesizing and investigating a new dimension of nanomaterials with a wide range of applications.