Owning to their superior electronic and optical properties, silicon nanomembranes (NMs) have attracted considerable attention to be exploited as fundamental building blocks for the applications in electronics, photonics, and optoelectronics. Nevertheless, small photon traveling distance in such ultra‐thin silicon (UT‐Si) nanomembranes with nanoscale thicknesses (50 nm) induces low total light absorption, which is crucial for optoelectronic applications. Here, a convenient and controllable strategy, involving self‐assembly of dielectric polystyrene (PS) microsphere array on UT‐Si, was proposed to enhance optoelectronic responses of UT‐Si‐based photodetectors in broadband. Scattering effect of PS microspheres facilitates to couple incident light into UT‐Si layer, thus enhancing the light absorption. UT‐Si‐based metal‐semiconductor‐metal (MSM) photodetectors with a PS microspehere array demonstrate significant enhancement in optoelectronic response compared with the photodetector without PS microspeheres. Furthermore, the response spectrum can be controllably tuned by adjusting the size of paved microspeheres. This research may provide a practical and cost‐efficient approach for enhancing the optoelectronic responses of nanomaterials with nanoscale thicknesses, thus expediting their potential applications in optoelectronic devices.