Windows of traditional wide band gap photodetectors are limited by the band gap of the semiconducting material used. In order to address this issue, the photoelectric properties of a plasmonic hot-electron phototransistor were fabricated and investigated. We have developed a plasmonic hot-electron phototransistor using a heavily doped silicon wafer as the back gate and insulating layer. Gold nanoparticles (AuNPs) were fabricated on the surface of the insulator via thermal annealing and the plasmonic hot-electron indium gallium zinc oxide (IGZO) phototransistor was developed. We investigated the optical and electrical properties of the phototransistor. The results revealed that the presence of AuNPs increased the photocurrent by a factor of 2.2 under a gate voltage of 90 V as compared to the IGZO phototransistor without AuNPs. The plasmonic hot-electron structure can effectively adjust the spectral response range of the phototransistor. Regulation of the back gate voltage was observed to amplify the photocurrent and improve the quantum efficiency of the device.