Hg1−xCdxTe metal‐insulator‐semiconductor (MIS) devices withx&bartil;0.22 often exhibit very short storage times that are determined by minority‐carrier dark currents. This study describes a novel system, for measuring the fast collapse of such devices. The measurement and modeling of the dark current during the fast collapse process is presented. A quantitative correlation is noticeable between the experimental results and theoretical calculations which assume that thermal‐trap‐assisted tunneling is the dominant dark process. The results demonstrate the importance of trap‐assisted tunneling in narrow band‐gap HgCdTe, and that this process causes short storage times.