It is expected that the blooming of the so-called Internet-of-Things (IoT) will depend on the availability of inexpensive, reliable and compact energy harvesters. Thermoelectricity features key advantages of reliability and is complementary to other sources but it’s efficiency is intrinsically limited to a few percent around room temperature and usually relies on harmful materials. Two decades of research on low-dimensionality materials have shown the potential of quantum dots, nanowires, thin films [1] or nano-composite materials towards reduced thermal conductivities and increased thermoelectric efficiency. It has been advocated that silicon thin-films, patterned through a so-called phonon engineering approach [2], could reach competitive thermoelectric power densities [3]. In this work we present recent results of 100 nm thick silicon membranes patterned with a 60 nm pitch holey lattice integrated a series of thermopiles. Integrated Joules heaters are used as a heat sources in order to establish a lateral heat gradient in the membranes plane. We comment on the fabrication and characterization of these devices which are able to generate up to 2mW.cm-² under 45K temperature difference [4,5].