In some embodiments, an open-gate pseudo-conductive high-electron mobility transistor (PC-HEMT) includes a multilayer hetero-junction structure made of III-V single-crystalline or polycrystalline semiconductor materials. This structure includes at least one buffer layer and a barrier layer, and is deposited on a substrate layer. The PC-HEMT further includes a two-dimensional electron gas (2DEG) or two-dimensional hole gas (2DHG) conducting channel formed at the interface between the buffer layer and the barrier layer, source and drain contacts, either ohmic or non-ohmic, connected to the 2DEG or 2DHG conducting channel, electrical metallizations for connecting the PC-HEMT to an electric circuit, and an open gate area between the source and drain contacts. Some embodiments use non-ohmic contacts, have thickness of the top (buffer or barrier) layer in the open gate area in the range of 5-9 nm, which corresponds to the pseudo-conducting current range between normally-on and normally-off operation mode of the transistor, and have the roughness of the surface barrier layer in the range of about 0.2 nm or less.