Using atomic force microscopy (AFM), we experimentally examined the features of field-electron emission from a single point-type silicon cathode into a quasi-vacuum (air) medium. In the non-contact AFM operating mode, the current – voltage characteristics (CVCs) of a single cathode with a nanometer radius of curvature of the tip were measured at distances of 10 nm and 20 nm between the cathode tip and the top of the measuring probe. The electric field distribution was simulated both on the surface of the tip of a single cathode and on the surface of the tips of individual cathodes within the array, based on which a theoretical estimate of the field enhancement factor as a function of the cathode-probe distance was made. The field-enhancement factor calculated from the experimental CVCs in the Fowler-Nordheim coordinates is several orders of magnitude higher than its value obtained from theoretical calculations. Such a mismatch between the experimental data and the simulation results indicates the need to take into account additional quantum-size effects, which play an important role in the formation of the field-electron emission current in the nanoscale gap. In particular, deformation of the silicon emitter tip can occur at this scale due to the penetration of a strong electric field into its surface region, which, in turn, causes the distortion of the potential barrier at the interface with the quasi-vacuum medium.