We fabricated field effect transistors having independent ohmic contacts to individual two-dimensional-electron gases in a double quantum well structure by etching the backgate (BG) area to 30 μm-thick, while keeping the major part of the substrate thick for ease of handling (60 μm). By this approach, it was made possible to form independent ohmic contacts with applied voltage to BG of about -60 V. We investigated the device by measuring the tunneling conductance as a function of temperature, in-plane magnetic field and carrier density. The temperature dependence showed that the broadening of resonant tunneling peak originated from the ionized impurity scattering and the electron-electron scattering. The in-plane magnetotunneling has shown two peaks at particular fields expected from the carrier densities in each well. These results indicate that the uniformity of the thickness of the etched BG area is good enough to allow the study of 2D-2D tunneling spectroscopy.