The electrical properties of hydrogen-terminated silicon (H-Si) surfaces were investigated by the assembly and testing of reliable and reproducible mercury-silicon junctions. When a H-Si surface is exposed to air under ambient conditions, the current density-bias voltage curve of the thus formed mercury-silicon junction initially maintains ohmic characteristics for a period of 8-12 h and then evolves to diode behavior. The current density substantially decreases, but can be recovered to a certain extent upon sonication in organic solvents. In agreement with infrared spectroscopic results, organic contamination of H-Si is suggested to play an important role in the transition of the electrical properties.