PbTe based semiconductors are characterized by a narrow energy gap and can be used for IR detectors, light emission diodes, lasers and thermoelectric devices. The objective of the present work was to study the effect of oxidation on the properties of n- and p-type PbTe samples prepared by powder metallurgy (bulk materials) and physical vapor deposition (thin films with thickness ∼1 μm). The samples were characterized by SEM, AES and XRD. The Hall effect and electrical conductivity of PbTe samples have been examined over the 80 – 300 K temperature range. The experimental results are accounted for in the framework of a model that is based on: 1- the fast diffusion of oxygen along grain boundaries (GB); 2 - oxygen absorption that generates acceptor states at GB (short time annealing) and the growth of PbTe oxides on GB with properties corresponding to wide band semiconductor (lengthy annealing); 3 - the creation of potential barriers on GB due to oxidation with a thermally activated dependence of the conductivity.