A Se chemical passivation [(NH4)2S+Se] for GaAs Schottky diodes is presented. We have found that our (NH4)2S+Se passivated Schottky diodes have more than one order of magnitude higher forward current density than the (NH4)2Sx passivated ones. In rapid thermal annealing treatment, an initial decrease and then increase of forward current density for (NH4)2Sx passivated diodes is observed. For the (NH4)2S+Se and (NH4)OH treated diodes, a steady decrease of Schottky barrier height with increased annealing temperature is observed. With or without annealing treatment, the (NH4)2S+Se passivated diodes have the lowest barrier height.