Measurements of the junction characteristics and the transport properties on either side of a vacuum‐cleaned siliconp‐njunction have been carried out. The changes in these properties during the adsorption of oxygen and hydrogen have also been investigated. In the clean condition, the value of (EF−EV) for both 21.5 ohm‐cmntype and 27 ohm‐cmptype was found to be 0.13–0.14 ev. When the silicon surface was clean, a large excess current across the junction was observed which disappeared during the adsorption of gas.