Ga2O3 nanowires on silicon substrates were synthesized by the chemical vapor deposition method, and the Ga2O3-based metal–semiconductor–metal structured solar-blind photodetector was constructed successfully. Anomalously, the as-constructed photodetector exhibits negative photoconductivity under the illumination from 365 to 645 nm (sub-bandgap excitation) while it shows positive photoconductivity at the 254 nm illumination (super-bandgap excitation), which indicates that the photodetector has a wide spectral response extending to visible light. Under 365 nm illumination, the ratio of dark current to photocurrent, responsivity, and detectivity of the photodetector reach 5570, 0.2 A/W, and 2.52 × 1011 jones, respectively. A possible mechanism is proposed to explain the rare negative photoconductivity phenomenon. Herein, because the negative photoconductivity occurs in sub-bandgap excitations, the photodetector can detect photons whose energy is less than the bandgap of the sample, widening the spectral response. This work provides a method for wide spectrum photodetectors and other negative photoconductivity devices.