We present investigations of the spatial distribution of space charges inthin films of conjugated polymers. A thermal wave method, the laserintensity modulation method, has been used to resolve the depth profile ofspace charges and the distribution of the internal electric field in 3–4 μ mfilms of poly(2, 5-pyridinediyl). The dynamics of the space-charge accumulationhas been investigated by means of measurements of the temporal evolution andthe temperature dependence of the pyroelectric response. The results demonstratethat in conjugated polymers, space charges of either sign can be storedpermanently by deep trapping. This charge significantly reduces the internalelectric field in the bulk of the films.