Bistable behavior of single Si dopants in the (110) surface layer of GaAs was studied with a scanning tunneling microscope (STM). The Si atom acts as either a positively charged substitutional donor or a negatively charged interstitial. Its configuration can switch under the influence of a local biasedSTMtip. To independently manipulate the charge state, the sample was illuminated by a laser during STM operation. The Si atom can be reversibly switched between its positive and negative charge states by turning the laser on and off, respectively. This process occurs mostly with the photon energy tuned above the band gap of GaAs, indicating that photogenerated electron-hole pairs play an important role in the process. The occupation of the donor and interstitial configurations depends on the carrier dynamics, i.e., the possibility of the electrons to escape or to be captured. If the tip-induced band bending is large enough, it is possible for electrons to tunnel into the conduction band and the donor configuration is observed. Another escape path is created when the sample is illuminated and photogenerated holes can recombine with the bound electrons of the dopant.