The effects of thermal annealing below 500 degrees C on Spindt-type molybdenum field emitter arrays were studied through the field emission characteristics and Mo surface analysis. The anode current of the field emitter arrays increases with increasing annealing time and then saturates after a certain period that is shorter for higher-temperature annealing. These phenomena are clearly explained by the molybdenum trioxide (MoO3) desorption revealed by studies using x-ray photoelectron spectroscopy and temperature programmed desorption, and by calculation of MoO3 desorption rates. The MoO3 desorption is the predominant effect for low-temperature annealing and the increase in the anode current is mainly due to lowering of the work function after MoO3 desorption.