A semi-fluidized bed is characterized by a combination of packed bed or fixed bed at the top and fluidized bed at the bottom within a single contacting vessel. Such a bed has advantages of both packed and fluidized beds. Various authors have studied the hydrodynamics, mass transfer, reaction kinetics of semi-fluidized beds of two phases and few studies in three phases. In the present study hydrodynamic characteristics viz. onset (minimum) semi-fluidization velocity of a co-current gas-liquid-solid semifluidized bed have been studied using liquid as continuous phase and gas as discrete phase. Experiments have been conducted in a 100 mm ID, 1.8 m height vertical Perspex column using air, water and glass beads in order to develop a good understanding of each flow regime in gas-liquid-solid semi-fluidization. It is found that minimum liquid semi-fluidization velocity increases with bed expansion ratio and decreases with superficial gas velocity.