Chemical vapor deposited SiO2 has previously been shown to form a useable insulator for InP MIS devices. In this paper possible reactions between Si, SiO, SiO2, O2, and InP and its oxides are investigated by calculation of the change in enthalpy of the reactions. The calculations indicate that no reaction is expected between SiO2 and InP or its oxides. However, both Si and SiO reduce the oxides of In and P. The reaction between InP and Si appears to be weak but possible. The various methods of depositing SiO2 are also examined in order to predict which of these methods is the least likely to cause reaction between the substrate and the depositing species.