A systematic study of the stability of CdTe solar cells fabricated by SCI and NREL has been made. Cells were stressed at elevated temperatures under various bias conditions, both with illumination (∼2 suns) and in the dark. An activation energy of approximately 1 eV is implied from cells stressed at various elevated temperatures. The stability of CdTe solar cells was found to be bias dependent and device-specific. Cells made with thick CdTe and no back-contact copper as well as by at least one SCI recipe were very stable. Extrapolation of effects assuming Arrhenius behavior yields estimated lifetime expectations for the cells stressed at elevated temperatures. ©1999 American Institute of Physics.