MKS Instruments, Andover, Mass., announced the closing of its acquisition of On-Line Technologies, a supplier of measurements and control products used for gas analysis, wafer metrology and process control based in East Hartford, Conn. Under terms of the agreement announced March 16, 2001, the acquisition transaction includes approximately 660,000 shares of MKS stock, contingent payments of approximately $1.5 million and assumption of On-Line debt of approximately $9.2 million. On-Line is the sixth acquisition since going public in 1999, and is part of the company's ongoing strategy to broaden its product and technology portfolio and its commitment to provide a suite of leading edge, best-in-class products.