A pyramidal shaped GaAs (tip-GaAs) photocathode for a polarized electron source (PES) was developed to improve beam brightness and negative electron affinity (NEA) lifetime by using field emission. The emission mechanism also enables the photocathode to extract electrons from the positive electron affinity (PEA) surface, and relax the NEA lifetime problem. I-V characteristics of electrons extracted from tip-GaAs shows that the electron beam was extracted by field emission mechanism, because a linear dependence was obtained in Fowler-Nordheim (F-N) plot. Furthermore, a tip-GaAs cathode has succeeded in generation of spin polarized electron beam. The polarization degree of tip-GaAs is about 34% at excitation photon energy of 1.63eV which is no less than that obtained by an NEA-GaAs cathode.