The sensor properties of semiconducting strontium titanate can be modified by dopants. On the one hand, the ambiguous dependence of the electrical conductivity on the oxygen partial pressure can be changed by a small lanthanum (donor) concentration to an unambiguous one over a wide oxygen partial pressure range. Polycrystalline Sr_0.995La_0.005TiO₃ and/or thick films have response times of few milliseconds, caused by a surface type mechanism of the conductivity. The bulk type mechanism is very slow and is responsible for the long-term behaviour. On the other hand, the temperature dependence of strontium titanate can almost be suppressed for a small oxygen partial pressure range by a high iron (acceptor) content. On the basis of SrTi_0.65Fe_0.35O₃ a fast thick film oxygen sensor is proposed, which can be applied to control of lean-burn engines.