Photovoltaic MoS2/Si nanowire array (SiNWA) heterojunction photodetectors (PDs) are constructed and investigated, which exhibit excellent photoresponse properties to light illumination at wavelengths from the deep ultraviolet to the near-infrared. Further photoresponse analysis reveals that a high responsivity of 53.5 A/W and a specific detectivity of 2.8 x 10(13) Jones, as well as fast response speeds of 2.9/7.3 mu s at 50 kHz are achieved in a MoS2/SiNWA heterojunction device. The high performances could be attributed to the high-quality heterojunction between MoS2 and the SiNWA. Such high performances of MoS2/SiNWA PDs are much better than those of previously reported MoS2-based PDs, suggesting that MoS2/SiNWA heterojunction devices have great potential in optoelectronic applications.