1. A thin film semiconductor device comprising: a substrate including at least one surface which is of a insulating dielectric material, a plurality of overlying layers of doped monocrystalline semiconductor material united to the insulating dielectric material, said doped monocrystalline layers being converted doped polycrystalline semiconductor material, a plurality of circuit elements in the layers, selected trenches isolating the circuit elements from each other, an insulating layer on the surface of the overlying layers and on the vertical surfaces of the trenches, and a metallization pattern contacting the circuit elements through the remaining trenches whereby a full dielectric isolation of the circuit elements is achieved in the device.