We have investigated the relation between the work function and corresponding quantum efficiency during the negative electron affinity (NEA) activation processes of GaAs surfaces qualitatively and determined the regions of positive electron affinity (PEA) surface and NEA surface. We found that the two surface states of NEA and PEA were switched during the alternating supply of Cs and O2 in the NEA activation sequence. After the supply of O2 following Cs deposition onto the clean GaAs, the surface still showed the PEA state for a few minutes and changed to the NEA state with increase of electron emissions. It should be noted that once the NEA surface was formed, there were two regions where the quantum efficiency continued increasing, both with and without changing the shape of spectrum. As one possibility, we believe that the increase in quantum efficiency is related to the number of electron emission sites and that there are various electron emission structures.