A new experimental measurement methodology was proposed to characterize the hydrodynamics in gas-liquid-solid semifluidized beds. Using pressure drop measurements in the lower fluidized bed section and a tracer response technique in the upper fixed bed portion, the six phase holdup components of the reactor were determined simultaneously. Available models for macroscopic predictions Of holdups, initially proposed for three-phase fluidization, were extended, and their applicability was discussed concerning semifluidized beds, Special attention was paid to the parameters of the generalized bubble wake model and their predictability with an artificial neural network. Phenomenological observations identified an additional interface region between both beds, which, viewed as an inchoate freeboard region determines the mechanisms of attachment and release of particles from the fluidized bed to the fixed bed portion.