The superconducting state in p-type Si single crystal backed with a Pb-In alloy has been studied by electron tunneling spectroscopy. The superconducting pair potential in the Pb alloy can be reduced either by an increase in the boron impurity concentration in the Si or by the accumulation of carrier concentration in the Si due to the electric field effect. The presence of the superconducting pair potential is also observed in the Si, and its pair potential is enhanced by an increase in the boron impurity concentration. These facts provide evidence for the superconductivity induced in the Si by the proximity effect, which is dependent on carrier concentration.