Abstract: Since late 1990s, high-quality nonmagnetic semiconductor heterostructures have shown a way to experimentally simulate magnetic interactions with gate-confined quantum dot nanostructures. By applying electrostatic potential to the gates, tunability of magnetic interaction was demonstrated, although technical difficulties had restricted the experiments to just one or two magnetic atoms. Here we show that in GaAs/AlGaAs-based III-V semiconductors an array of localized spins naturally develop over a small window of gate voltage or charge density. Although the spins are associated with background potential fluctuations, we find that they are embedded in a quasi-regular manner within the 2D electron system (2DES), thereby indicating formation of a quasi-regular 2D Kondo-lattice. Subsequently, we have observed a gate-tunable duality of spontaneous magnetism and many-body coherent state within the 2D system, at the milliKelvin temperature range.