The photocapacitance (PHCAP) method in the constant capacitance condition has been applied to determine the energy and density of deep levels within the limits of a certain depletion layer thickness as a function of the photon energy and the applied voltage. Samples used were variousn‐type GaAs crystals annealed for a long time under excess As vapor pressure and rapidly cooled. The present PHCAP investigations have revealed several stoichiometry‐dependent deep levels including some photoquenching levels. These areEc−0.66 and −0.72 eV deep donors, the photoquenching level at 1.03, 1.25, and 1.41 eV. The As‐vapor‐pressure dependence of the density of these deep levels in quasithermal equilibrium were also clarified. The 1.25‐eV photoquenching level density increased monotonically with increasing applied As vapor pressure and finally saturated at extremely high As vapor pressures. The density ofEc−0.72 eV deep donors showed a similar dependence on the As vapor pressure, but showed less saturation under higher As vapor pressures. TheEc−0.72 eV deep donor is quite different from the so‐called EL2 level. But the temperature dependence of the PHCAP responses (&Dgr;Vph‐T) revealed strong interaction effects among these defect structures. From the photoluminescence results and conventional deep‐level transient spectroscopy measurements,it was clarified that bothEc−0.66 and −0.72 eV deep donors had larger Frank–Condon shifts, 0.28 and 0.24 eV, respectively, compared with that of the so‐called EL2 level (0.12 eV). The PHCAP measurements after photoexcitation were carried out to detect de‐ionization of the photoionized deep levels. Additional de‐ionization of the photoionized state of the 1.41‐eV photoquenching level was detected adjacent to those of the EL2 level. These de‐ionization could be detected only in the course of the photoquenching phenomenon inn‐type GaAs. The As‐vapor‐pressure dependence of these deep levels shows that interstitial As atoms play a vital role in forming deep levels in annealed GaAs crystals.