Chips having rear contacts connected by through vias to front contacts

A microelectronic unit is provided in which front (102) and rear (114) surfaces of a semiconductor element (100) may define a thin region (105) which has a first thickness and a thicker region having a thickness at least about twice the first thickness. A semiconductor device (112) may be present at the front surface, with a plurality of first conductive contacts (116) at the front surface connected to the device. A plurality of conductive vias (125) may extend from the rear surface through the thin region (105) of the semiconductor element to the first conductive contacts (116). A plurality of second conductive contacts (134) can be exposed at an exterior of the semiconductor element (100). A plurality of conductive traces (126) may connect the second conductive contacts (134) to the conductive vias (125).