The authors investigate the non-linear excitation of ion-acoustic oscillations in a plane plasma layer contained by an external high-frequency electromagnetic field of the TE wave type. The plasma is assumed to be collision-free and non-isothermal (Te » Ti). The time-averaged density distribution in the plasma layer is found. The conditions are ascertained for the resonance excitation of ion-acoustic waves at the second harmonic of the external field; near the resonance, the amplitudes of the excited waves can be fairly large, not only within the skin layer but also through the entire plasma volume.