The evolution of an arbitrary initial nonequilibrium distribution of electrons and electric fields is investigated in a structure consisting of semiconfined media, viz., plasma and insulator (vacuum). The comprehensive spectrum of potential oscillations of electric fields is obtained. It is shown that the set of frequency eigenvalues is determined by the properties of the electron distribution function in equilibrium and perturbed states. In a cold plasma, volume and surface oscillations with the Langmuir frequency can propagate along with surface plasmons, while only a surface plasmon field exists in the insulator. In the presence of spatial dispersion, all types of volume and surface oscillations emerging in the plasma are emitted to the insulator. In addition to the field of intrinsic oscillations, an electric field of anomalous penetration associated with the effects of ballistic transport of conduction electrons at low temperatures also exists in the plasma. For a cold plasma, delay effects are taken into account, and the spatial and time distributions of the fields in the insulator are found. ©1998 American Institute of Physics.