p‐GaAs (110) surfaces activated to negative electron affinity (NEA) have been examined with photoelectron spectroscopy. A typical activated GaAs surface is found to consist of both a layer of oxygen bonded to GaAs and a (Cs+,O−2) layer. The GaAs‐O layer was not anticipated prior to this work. A GaAs‐O‐Cs dipole plus the polarization of a Cs+‐O−2‐Cs+sandwich layer is proposed to explain the NEA condition based on the structure of activated surfaces found in this work. The identification of the O‐GaAs bonding layer explains the better yield achieved by the two‐step activation process compared to that achieved by a single‐step process. Possible optimization of the activation process by forming the O‐GaAs layer and the (Cs+,O−2) layer is also discussed. Adsorption of OH from the residual gas in an ultrahigh vacuum chamber is identified as one degradation mechanism of the GaAs photocathodes.