A simple theory that makes it possible to calculate the characteristics of metal–insulator–thin metal film tunnel junctions is developed. Along with the well-known oscillations in the voltage dependence&sgr;(V)of tunneling conductance due to commensurate states, it predicts a number of new effects. For example, even in the case of a symmetric tunnel junction formed by the identical materials with a rectangular potential barrier, the&sgr;(V)curve displays a noticeable asymmetry. The branch of the&sgr;(V)curve corresponding to tunneling to the thin-film electrode contains a structure consisting of conductance dips. ©1998 American Institute of Physics.