A microelectronic unit 400 can include a semiconductor element 401 having a front surface, a microelectronic semiconductor device adjacent to the front surface, contacts 403 at the front surface and a rear surface remote from the front surface. The semiconductor element 401 can have through holes 410 extending from the rear surface through the semiconductor element 401 and through the contacts 403. A dielectric layer 411 can line the through holes 410. A conductive layer 412 may overlie the dielectric layer 411 within the through holes 410. The conductive layer 412 can conductively interconnect the contacts 403 with unit contacts.