We consider an electron-hole system in double quantum wells theoretically. We demonstrate that there is a temperature interval over which an abrupt jump in the value of the ionization degree occurs with an increase of the carrier density or temperature. The opposite effect -the collapse of the ionized electron-hole plasma into an insulating exciton system -should occur at lower densities. In addition, we predict that under certain conditions there will be a sharp decrease of the ionization degree with increasing temperature -the anomalous Mott transition. We discuss how these effects could be observed experimentally.PACS numbers: 71.35.Ee, 73.21.Fg It was suggested by Mott [1] that an increase of the temperature or density of an insulating system of excitons may lead to avalanche ionization as a result of screening and k-space filling. Despite significant efforts [2,3,4,5,6], there is still no firm theoretical understanding of this effect, and the existence of the transition is disputed.In bulk indirect-bandgap semiconductors, experimental observation of the Mott transition is prevented by the formation of electron-hole liquid (EHL) droplets [7]. The absence of low-temperature phase transitions in direct semiconductors and single quantum wells is believed to be caused by fast radiative recombination, which does not allow enough time for the photo-generated electron-hole plasma (EHP) to cool down.In recent years there has been increased attention towards double quantum wells (DQWs) -heterostructures containing two quantum wells (QWs) situated close enough so that the Coulomb correlations between particles in different QWs are significant. Electrons and holes from adjacent QWs form spatially indirect excitons (IXs) with very long lifetimes, due to the small electron-hole (e-h) wavefunction overlap. The experimentally confirmed long life-time and stability of the DQW indirect exciton [8,9,10,11,12] suggests that the formation of a medium-density cold exciton gas is possible. Under certain conditions this gas may undergo a Mott transition.Another property beneficial for observation of the Mott transition in a DQW is that the spatially separated EHP posses substantial electrostatic energy (Hartree term in the self-energy). This leads to the fact that for large enough separation of quantum wells there is no minimum in the dependence of the ground-state energy on the density, and thus the formation of e-h droplets is not possible [5,13].The purpose of this Letter is to investigate the possibility of a Mott transition in DQW systems and to encourage further experimental research.The main theoretical difficulty in investigation of the Mott transition is that it is inherently a medium-density effect, for which low-density and high-density approximations do not work. The correct approach would require careful handling of the Coulomb interaction depending on the thermodynamic state of the system, which implies a self-consistent procedure.Before studying the Mott transition, which is essentially a jump in the ionization...