A photoinduced “transient thermoelectric effect” (TTE) has been measured for ap-GaAs crystal using a tunable pulsed laser, over the laser energy range 0.93–1.80 eV, laser intensity0.2–130 mJ/cm2,time range 1 ns–1 ms, and temperature range 4.2–50 K, with special attention to native defects of EL2 centers, whose ground state(EL20)and excited state(EL2ex)are located, respectively, at 0.76 and 1.80 eV above the top of the valence band (their energy difference&sgr;ex=1.04 eV). After laser irradiation at one end of the sample, a TTE voltage is induced within a rising time&tgr;r(1.0–1.5 &mgr;s) due to hole diffusion, followed by exponential decay with multiple decay times&tgr;1–&tgr;5that depend on the laser energy, its intensity, and the temperature. The decay time&tgr;1is assigned to relate to photoexcited electron diffusion in the conduction band and others&tgr;2–&tgr;5with electron recombinations with photogenerated holes in the valence band via EL2 centers inp-GaAs, for which a rough evaluation of the capture cross section is made. Based on the experimental data, we have discussed the photoinduced carrier generation/recombination processes in three laser energy ranges with the two boundaries&sgr;exand the band-gap energyEg(=1.50 eV); regions I(E<&sgr;ex),II(&sgr;ex⩽E<Eg),and III(E⩾Eg).For these three energy regions, we have carried out computer simulations for the photoinduced TTE voltage profiles by solving one-dimensional transport equations for photogenerated electrons and holes, in qualitative agreement with the observations. ©1997 American Institute of Physics.