Background and Objectives: The laws governing the modification of the current-voltage characteristics of the metal-insulatorsemiconductor structures due to the formation of embedded surface potentials are investigated. Surface potentials are formed when an atomically clean surface of silicon crystals is produced using microwave plasma micromachining. The aim of the work is to study the effect of plasma micromachining in various chemically active gaseous media on the properties of silicon MIS structures. Materials and Methods: In the experiments, silicon (100) crystals of various types of conductivity with a specific resistance of 0.01 ... 0.02 Ohm · cm were used. After low-energy microwave plasmachemical etching in freon-14 or argon medium, the sequentially sealing tunnel-thin (10–20 nm) silicon carbide layer and silicon dioxide layer of 0.5 microns thick were deposited on the gate region of the structure in the same technological cycle. A layer of amorphous silicon with a thickness of 20 nm was deposited on the drain and source. Then metal contacts were applied to all areas. The measurement data were recorded using the ADC. The supply voltage was carried out using a two-channel block ATTEN APS3005S-3D. Results: With a positive polarity at the gate of the MIS structure, minority charge carriers in the p-type semiconductor tunnel into trap centers at the crystal boundary, partially neutralizing the applied external potential. Since the built-in spatial potential is larger during etching in the argon plasma than that with plasma-chemical etching in the freon-14 medium, the weakening of the external field is greater in the case of argon. In the case of plasma processing of n-type silicon crystals in the medium of freon-14, the negative total gate field is less than after the treatment in the argon medium. Conclusion: The influence of the built-in surface potential on the slope of the VAC of MIS devices based on silicon crystals of various types of conductivity, as well as their asymmetry upon changing the polarity on the gate can be used, for example, when creating specialized information recording and reading devices, TVS diodes with asymmetric direct and reverse branches VAC, other devices and devices of the nanosystem technology.