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Compensation of intrinsic charges is widely used to reduce the bulk conductivity of 3D topological insulators (TIs). Here we use low temperature electron irradiation-induced defects paired with in situ electrical transport measurements to fine-tune the degree of compensation in Bi 2 Te 3 . The coexistence of electrons and holes at the point of optimal compensation can only be explained by bulk carriers forming charge puddles. These need to be considered to understand the electric transport in compensated TI samples, irrespective of the method of compensation. 0 18 (sample A) and4.4 10 19 cm −3 (sample B), respectively, as a function of electron dose Q. Similar to room temperature irradiations [11], r xx shows a maximum, which at low temperature amounts to an increase by three orders of magnitude. The maximum values of 74 and 90 mΩcm for samples A and B, respectively, are comparable to those obtained on non-metallic Bi 2 Te 3 samples (12 mΩcm) cut from crystals grown with a weak OPEN ACCESS RECEIVED