  Transport characteristics of single crystal bismuth films on Si(111)-7 \times
7 are found to be metallic or insulating at temperature below or above TC,
respectively. The transition temperature TC decreases as the film thickness
increases. By combining thickness dependence of the films resistivity, we find
the insulating behavior results from the states inside film, while the metallic
behavior originates from the interface states. We show that quantum size effect
in a Bi film, such as the semimetal-to-semiconductor transition, is only
observable at a temperature higher than TC. In addition, the metallic interface
state is shown to result from the large SO-splitting at interfaces.
