A multi-chamber type process system for processing semiconductor wafers is constituted such that a plurality of units selected from process units, transfer units, interconnection units and in/out units are connected via gate valves. Each of the units has a casing with one or more openings through which each of the wafers passes. The gate valve is attached to a flange provided at the opening, thereby connecting the openings openably and air-tightly. The openings are situated such that the units are connected in a direction defined in units of substantially 90.degree., and the direction of transfer of the wafers is defined in units of substantially 90.degree.. Those of the openings of the casings of the units, which are not connected to the other openings of the casings, are air-tightly closed by blind plates such that the casings of the units form a vacuum chamber. The internal pressure of each of the casings of the units can be independently controlled.