This article describes an experimental study of the electrical and kinetic parameters of a Knudsen-mode thermionic converter (TIC) equipped both with a multicavity and a smooth emitter that converts heat into electrical energy using a combination of cesium and barium vapors. In the study, we recorded and analyzed data on how the maximum electron current density and the specific power are affected by the values of cesium and barium vapors pressure, the width of the interelectrode gap, and such parameters of the emitters as temperature and surface geometry. By analyzing the influence of surface geometry, it was revealed that the values of the electron current density and the electric power are four times higher in a TIC with a multicavity emitter compared to a TIC with a smooth emitter. TIC efficiency was analyzed taking into account the effective emissivity of the multicavity emitter. It is shown that the efficiency of such a TIC exceeds that of a TIC with a smooth emitter despite a slight increase in heat transfer from the emitter to the collector due to radiation.