Temperature tuning and stability of nonlinear optical devices employing CdSe and ZnGeP2are considered for the first time. From the measured refractive index data at room temperature and the corresponding appropriate temperature derivatives, Sellmeier coefficients are found for the evaluation of refractive indexes both below and above room temperature. These can be used to calculate phase-matching angles at different temperatures. We have evaluated temperature stability of phase-matching angles in tunable parametric oscillators and down-converters and also in up-converter operations which have been reported at room temperature. Temperature characteristics have been worked out for tunable generation of radiation near the 16 μm region in CdSe and the type II second-harmonic generation has been found to be possible for temperatures C in ZnGeP2because of its positive temperature coefficient in birefringence.