A method of fabricating a microelectronic unit, comprising: providing a microelectronic element including a semiconductor region of monocrystalline form, the microelectronic element having a front surface , a rear surface remote from the front surface , a front contact exposed at the front surface , an active circuit element adjacent to a front monocrystalline semiconductor region surface, a region of polycrystalline semiconductor material disposed in a trench formed in the monocrystalline semiconductor region from a front surface of the monocrystalline semiconductor region and extending towards the rear surface , the polycrystalline semiconductor material being insulated from the monocrystalline semiconductor region by a dielectric region , and a via disposed entirely between the front surface and the rear surface of the microelectronic element , the front contact being electrically coupled with the region of polycrystalline semiconductor material through the via ; forming an opening extending from the rear surface partially through a thickness of the monocrystalline semiconductor region by removing a portion of the monocrystalline semiconductor material, the opening exposing the region of polycrystalline semiconductor material ; removing at least a portion of the polycrystalline semiconductor material through the opening ; forming a conductive region at least partially replacing the removed polycrystalline semiconductor material; and forming a rear contact (168; 268; 568) electrically coupled with the conductive region and exposed at the rear surface for electrical connection with a circuit element. providing a microelectronic element including a semiconductor region of monocrystalline form, the microelectronic element having a front surface , a rear surface remote from the front surface , a front contact exposed at the front surface , an active circuit element adjacent to a front monocrystalline semiconductor region surface, a region of polycrystalline semiconductor material disposed in a trench formed in the monocrystalline semiconductor region from a front surface of the monocrystalline semiconductor region and extending towards the rear surface , the polycrystalline semiconductor material being insulated from the monocrystalline semiconductor region by a dielectric region , and a via disposed entirely between the front surface and the rear surface of the microelectronic element , the front contact being electrically coupled with the region of polycrystalline semiconductor material through the via ; forming an opening extending from the rear surface partially through a thickness of the monocrystalline semiconductor region by removing a portion of the monocrystalline semiconductor material, the opening exposing the region of polycrystalline semiconductor material ; removing at least a portion of the polycrystalline semiconductor material through the opening ; forming a conductive region at least partially replacing the removed polycrystalline semiconductor material; and forming a rear contact (168; 268; 568) electrically coupled with the conductive region and exposed at the rear surface for electrical connection with a circuit element. <EOS>