The invention relates to the fabrication of electronic circuits on a thinned semiconductor substrate. To produce a connection pad on the back side of the thinned substrate, the procedure is as follows: an integrated circuit is produced on an unthinned substrate, in which a portion of a polycrystalline silicon layer (18) dedicated for the connection of the pad is provided. The circuit is transferred onto a transfer substrate (30) and then its back side is thinned. A via is opened in the thinned semiconductor layer (12) in order to gain access to the polycrystalline silicon; aluminum (80) is deposited and this layer is etched so as to define a pad which is in contact with the internal interconnects of the integrated circuit by way of the polycrystalline silicon.