A simple and fast way to measure proton self-diffusion coefficients of small penetrant molecules in semicrystalline polymers is introduced. The approach takes advantage of the strong static gradient of a mobile single-sided NMR sensor and it is demonstrated on PE samples with varying degrees of crystallinity fully saturated in either toluene or n-hexane. The self-diffusion coefficients were measured using the gradient stimulated echo sequence appended with a CPMG. It is also shown for the first time, with demonstration on PE plates several millimeter thick with different aging histories, that one-dimensional profiles of self-diffusion coefficients as a function of depth can be easily obtained.