ATLAS is designed to describe tests in terms that are independent of any specific test system, and has been constrained to ensure that it can be implemented on ATE. In this language, the semantics of signal statements is far different from that of the traditional programming languages. First, the performance of signal statements is to transmit the signals between the test devices and UUTs, according to which the ways of semantic description in the course of devices allocation are given; second, the transmission of the signals is realized by changing the state of test devices, then following the semantic description of device state which includes the state of device operation, the state of the device attributes and the connection state; last, the denotational semantics of the single-action signal statements are given based on the semantics of the device allocation and the state of test devices.