Fuel cells are formed in a single layer of conductive monocrystalline silicon including a succession of electrically isolated conductive silicon bodies separated by narrow parallel trenches etched through the whole thickness of the silicon layer. Semicells in a back-to-back configuration are formed over etch surfaces of the separation trenches. Each semicell formed on the etch surface of one of the silicon bodies forming an elementary cell in cooperation with an opposite semicell formed on the etch surface of the next silicon body ...