It is shown that the two-dimensional-electronic charge on the cathode surface gives the main contribution to emission currents measured in the nanosecond range. This made it possible to propose a new method for determining the effective mass, the de Broglie wavelength, the charge density, and the concentration of free carriers in the near-surface layer of the space charge region of the cathode. The efficiency and accuracy of the method has been proven for the cathode based on the shock-wave modified graphite by comparison of the estimates of the effective mass values of the free charge carriers with the data obtained by other methods.