The paper reports on InP and GaN Schottky diode hydrogen sensors prepared by printing colloidal graphite on InP and GaN with catalytic metal Pd, Pt or bimetal Pd/Pt nanoparticles (NPs), electrophoretic depositions of metal NPs on surfaces of semiconductor wafers were performed from isooctane colloid solutions prepared by reverse micelles technique with dioctyl sodium sulfosuccinate (AOT) surfactant. Deposited metal NPs were characterized by SEM. Current voltage characteristics of the diodes showed high rectification ratio (about 10⁷ at voltage 1V), low leakage currents and high Schottky barrier heights giving evidence of small Fermi level pinning. Currents changed by more than six orders of magnitude after diode exposures to 0.1% hydrogen in nitrogen, showing extremely high sensitivity of hydrogen detection. Time response of the current of forward voltage biased diodes to exposure of various concentrations of hydrogen in nitrogen was measured in the range from 1 to 1000ppm of hydrogen. The detection limit of hydrogen was estimated at 0.5ppm.