An apparatus for automatic semi-batch sheet treatment of wafers such as high-purity silicon semiconductor wafers by plasma reaction is disclosed. The apparatus comprises a wafer carrying mechanism, a reaction chamber with an opening at the bottom, a wafer table disposed beneath the opening and provided with a sub-table for mounting the wafer, and control devices for driving the above elements in linkage motion. The wafer carrying mechanism is substantially composed of a conveyor for carrying a wafer to be treated, a pair of open-close type wafer carrying wire conveyors which are spaced in parallel at a certain distance and open and close in linkage motion so that the wafer table may pass vertically therethrough to be fixed vacuum-tightly to the reaction chamber, a mechanism for opening and closing the wire conveyors and a treated wafer carrying conveyor. The subtable is vertically movable and capable of passing the wire conveyors when closed.