Colloidal InAs nanocrystals (NCs) were synthesized by heating an organometallic solution, containing triphenylarsine as the arsenic source. Because the triphenylarsine is quite stable in ambient conditions at room temperature, the reaction is easy to handle compared with conventional synthesis using tris (trimethylsilyl)arsine. The average size of InAs NCs obtained was varied in the range from 12 run to 20 run according to the reaction time, and their optical gap was larger than that of the bulk InAs because of quantum size effect. The reaction mechanism of InAs NCs formation was discussed based on the infrared absorption spectra of reaction solutions, and formation of a reaction intermediate was suggested during the long induction period, approximate to 80 min, of IRAs NCs formation. (C) 2014 Elsevier By. All rights reserved,