Transport characteristics of single crystal bismuth films on Si(lll)-7x7 are found to be metallic or insulating at temperatures below or above T_C,respectively.The transition temperature T_C decreases as the film thickness increases. By combining thickness dependence of the films resistivity,we find the insulating behaviour results from the states inside film,while the metallic behaviour 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 T_C. Transport characteristics of single crystal bismuth films on Si (lll) -7x7 are found to be metallic or insulating at temperatures below or above T_C, respectively. Transition temperature of Tc decreases as the film thickness increases. By combining thickness dependence of the film 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 T_C.