A shower head for adjusting distribution of a reactant gas in a process region of a semiconductor manufacturing reaction chamber, wherein a top plate has a gas port for introducing the reactant gas into the reaction chamber; a face plate, having through holes, disposed opposite the process region; a first baffle plate, having through holes, disposed between the top plate and the face plate and capable of moving up or down, wherein the first baffle plate has a top surface that defines a first gap for forming a first lateral flow passage; a second baffle plate, having through holes, disposed between the first baffle plate and the face plate and capable of moving up or down, wherein the second baffle plate has a top surface that defines a second gap for forming a second lateral flow passage; and a gap controller for determining widths of the first and second gaps.