To understand the thermochemistry and determine the rate limiting steps of ZnGeAs2 thin-film synthesis, experiments were performed to measure the (a) thermal decomposition rate and (b) elemental composition and deposition rate of films produced with pulsed laser deposition (PLD). The decomposition rate is kinetically limited with an activation energy of 1.08 +/- 0.05 eV and an evaporation coefficient of similar to 10(-3). We show that ZnGeAs2 thin film synthesis is a metastable process with the kinetically-limited decomposition rate playing a dominant role at the elevated temperatures needed to attain epitaxy. Our conclusions are in contrast to those of earlier reports that assumed the growth rate is limited by desorption and the resulting low reactant sticking coefficient. The thermochemical analysis presented here can be used to predict optimal conditions for ZnGeAs2 film physical vapor deposition and thermal processing. (C) 2011 Elsevier B.V. All rights reserved.