We report a high-performance InAs nanowire phototransistor with the photoresponse mechanism governed by the gate-controlled surface states. Detailed characterizations suggest that the high density of surface defect states of the InAs nanowire can capture electrons from the nanowire core to form negative surface charge centers. Before and after light illumination, nanowire surface states undergo processes of capturing and neutralizing the electrons, respectively. This leads to an increase in the concentration and mobility of electrons after light illumination, which endows the device with remarkable photoresponsivity. After modulating the surface states through gate voltage and surface passivation, significantly high responsivity of up to 4.4 × 103 A/W and gain of up to 2.7 × 103 under the illumination of light at the wavelength of 2000 nm are obtained, putting our devices among the high-performance short-wave infrared nanowire photodetectors. This work provides an important reference for understanding the surface effects of nanomaterials and enhancing the performance of nanophotodetectors by modulating the surface states.