Three‐photon photoemission effect on GaAs–O–Cs negative electron affinity surfaces (NEA) was studied by using a nanosecond pulsed laser at 2.06 &mgr;m wavelength. The photocurrent densities from the photocathodes with different sensitivities were measured as a function of laser intensity at both room and liquid nitrogen temperatures (77 K). The dependence of photocurrent density on the light intensity shows a typical slope of three in logarithmic plot. The results are interpreted in terms of multiphoton photoemission (MPPE) effect. The influence of thermal electron emission to MPPE are discussed. ©1995 American Institute of Physics.