Abstract: Though the dynamic current testing can cover more faults than IDDQ,it requires a very high speed automatic test equipment （ATE） or a high quality sensor for on-line testing,which is not available at present.The method of at-speed current testing applies two alternative vectors to the circuits under test to enable the possibility for using a slow measurement and testing—at a high frequency operation.This paper proposes some techniques for fault collapsing for stuck-open faults,and their application to test generation for at-speed current testing.Experimental results show that the test generation efficiency is improved by 200times through employment of the fault collapsing techniques.