We propose and demonstrate a novel technique using focused Si ion beam implantation to produce high-quality mesoscopic channels. Low-energy Si implantation compensates the surface potential of a modulation-doped heterostructure that is designed to have no conductive channels at the heterointerface. The implantation forms a conductive channel separated from the damaged implanted region. The mobility of the channel is improved by decreasing the ion energy from 100 to 35 keV. Sub-μm to 5 μm wide channels fabricated by 35 keV Si+ ions show a mobility of 5.3×105 cm2/V s and a ballistic length of 3.1 μm at 1.5 K.