A process for forming an insulating layer of silicon dioxide in a silicon substrate that surrounds and electrically insulates a semiconductor device is disclosed herein. The process comprises the steps of forming a recess on the outer surface of the silicon substrate that encompasses the site of the semiconductor device by photo-resist patterned reactive ion etching, and then removing silicon on the surface of the resulting recess whose crystal structure has been damaged by the reactive ion etching. Next, dopant atoms are selectively deposited on the surface of the recess so that the surface of the recess might be rendered into a porous layer of silicon when immersed in hydrogen fluoride and subjected to an electrical current. Prior to the porousification step, silicon is epitaxially grown within the walls of the recess to form the site for a semiconductor device. The substrate is then immersed in hydrogen fluoride while a current is conducted through it in order to porousify the silicon between the device island and the rest of the substrate. Finally, the substrate is thermally oxidized in order to render the porous layer of silicon into a insulating layer of silicon dioxide. The provision of such individual insulating layers around each of the devices on the substrate allows the manufacture of a high density and radiation hard semiconductor array that is not susceptible to electrical current leakage between components.