We suggest a technique of fabrication of thick heavily Ga doped by thermomigration layers of Si for modern power electronics devices. Structure perfection and layers composition as a function of formation temperature were studied by techniques of X-ray Lang topography, X-ray rocking curves and secondary ion mass spectrometry. The fabricated layers are single crystalline, no mismatch dislocations were found on the interface with the Si substrate. The Ga concentration in the layers can be varied in the range (1.6-4.8)1019 cm-3, being higher than for Si doping with aluminum.