Variation of the electrophysical and structural parameters of GaAs-based pseudomorphic transistor heterostructures with an InGaAs channel during more than eleven-year storage in natural conditions have been investigated. It was found that the values of the electrophysical parameters remained within specified limits (taking into account measurement errors) after 11 years of storage. The structural properties (thickness and composition of the InGaAs channel) of pseudomorphic heterostructures have undergone significant changes associated with the InGaAs channel layer broadening due to atomic diffusion.