The Seebeck effect in ZnO (n-type) and CuO (p-type) nanowire bundles grown on alumina substrates has been investigated. By combining n- and p-type nanostructured elements, a planar thermoelectric device has been proposed and characterized, confirming the feasibility of fabricating planar thermoelectric generators based on metal oxide nanowires with the future aim of powering autonomous sensors and microsystems.