Borane-based electroless plating baths are of interest in many microelectronics applications such as barrier and capping layers for copper integrated circuit interconnect. To optimize the plating baths a thorough understanding of the role of the bath constituents is required. To this end we have employed microelectrodes to investigate the oxidation mechanism of boranes in alkaline solutions. In this paper we present data for the simpler ammonia borane (AB) oxidation and compare it with the previous analysis of dimethylamine borane (DMAB) oxidation. Both AB and DMAB are shown to oxidize in two steady-state mass transport-controlled oxidation waves for specific concentration ranges. Particular emphasis is placed on the analysis of the second oxidation wave observed at less negative potentials and the differences observed in the analysis of AB and DMAB in this potential region. The potential range for oxidation, the optimum concentration, and a suggested mechanism for oxidation are shown.