NOVELTY - A fuel cell comprises a half-cell formed on a conducting monocrystalline silicon substrate connectable to a load circuit. The parts of the half-cell comprises parallel trenches cut in a cell area defined on a surface of the silicon substrate through which a gas may be fed to the electrode of the half-cell.    USE - For integrated semiconductor device (claimed).    ADVANTAGE - The invention is of minuscule size realized on silicon, and can be at least partly integrated on a silicon chip containing an integrated circuit.    DETAILED DESCRIPTION - A fuel cell composed of a positive half-cell, comprises a microporous catalytic electrode permeable to a fuel gas and connectable through parts of the half-cell to an electric load circuit, a negative half-cell comprising a microporous catalytic electrode permeable to an oxygen containing gas and to products of the electrodic reaction and connectable through parts of the half-cell to the electrical load circuit of the cell, a cation exchange membrane separating the catalytic electrodes, and feeding mechanisms for feeding the fuel gas to the catalytic electrode of the positive cell and for feeding oxygen containing gas to the catalytic electrode of the negative half-cell and for exhausting products of the electrodic reaction. Each half-cell is formed on a conducting monocrystalline silicon (1, 2) substrate connectable to the load circuit. The parts of the half-cell comprises parallel trenches (7, 8) cut in a cell area defined on a surface of the silicon substrate through which a gas may be fed to the electrode of the half-cell.    An INDEPENDENT CLAIM is included for a process of fabrication of a half-cell of a fuel cell on a conducting monocrystalline silicon substrate comprising:    (i) procuring a p+ or an n+ doped monocrystalline silicon substrate with a dopant concentration of 1017-1019 atoms/cm3 and electrical conductivity of at most1 ohm-cm;    (ii) depositing a germ layer of gold, platinum, palladium, iridium, rhodium, ruthenium, and alloys of the metal(s) with a thickness of 20-60 nm on the substrate surface;    (iii) defining parallel strips (3, 4), using a resist mask, uniformly spaced from one another and galvanically depositing, using the germ layer as cathode, a metal belonging to the same group of metal to form metallic strips of a thickness of 5-30mum;    (iv) removing the resist mask and etching the metal until completely removing the germ layer;    (v) electrochemically eroding the substrate of doped silicon by polarizing it as anode in an electrolyte containing hydrofluoric acid causing anodic oxidation of silicon and a continuous dissolution of the silicon oxide to produce a porous heterogeneous columnar crystalline skeleton for a depth of 5-40mum in the substrate in the unmask area by the metal strips;    (vi) depositing an electrocatalytic metal of platinum, palladium, iridium, ruthenium, rhodium, and alloys of the metal(s) on the skeleton of doped silicon forming parallel microporous strips of catalytic metal electrically and mechanically connected to adjacent preformed metal strips; and    (vii) selectively etching the silicon in a basic solution until forming gas circulation channels underneath the metal strips using the preformed strips as mask.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross section of a micro fuel cell made on a monocrystalline silicon substrate.    Monocrystalline silicon (1, 2)    Parallel strips (3, 4)    Nonporous metal strips (5, 6)    Parallel trenches (7, 8)