  In order to determine the ratio of CKM matrix elements |V_{ub}/V_{cb}| (and
|V_{ub}|), we propose a new model-independent method based on the heavy quark
effective theory, which is theoretically described by the phase space factor
and the well-known perturbative QCD correction only. In the forthcoming
asymmetric B-experiments with microvertex detectors, BABAR and BELLE, the total
separation of b --> u semileptonic decays from the dominant b --> c
semileptonic decays would be experimentally viable. We explore the possible
experimental option: the measurement of inclusive hadronic invariant mass
distributions. We also clarify the relevant experimental backgrounds.
