Abstract: Si single crystal surface in vacuum deposition of organic semiconductor materials 3,4,9,10-perylenetetracarboxylic dianhydride （PTCDA） can form organic/inorganic heterojunction. The use of indium tin oxide （ITO） deposited on the surface as PTCDA incident light window,on its surface sputtering Al/Ni contact electrode,protection in an atmosphere of hydrogen by 350 ℃,3 minutes alloying,its specific contact resistance ρ_s=5.2×10^-5 ·cm. Use α level instrument,atomic force microscopy,UV-visible spectrophotometer and x-ray diffractometer,it’s a good low resistance ohmic electrodes formation process conditions and surface and interface are analyzed and discussed.