Semiconductor device

A semiconductor device including a port circuit (301) connected to an internal circuit, external terminals to which the port circuit is connected and a boundary scanning circuit (180, 18), the boundary scanning circuit being the one that makes access to the external terminals through the test access terminals. The test access terminals are also used as predetermined external terminals among the external terminals. Selection means (301, 303 to 307) are provided for selectively determining whether the multi-use terminals (P1 to P5) be connected to the port circuit or to the boundary scanning circuit, and for selecting, as an initial state, the state where the multi-use terminals are connected to the boundary scanning circuit in response to the power-on reset. Since the test access terminals need not be dedicated, the boundary scanning function can be furnished while guaranteeing pin compatibility of external terminals. When the boundary scanning function is not utilized or when the port function of the multi-use terminals is not used despite of using the boundary scanning function, complete compatibility is guaranteed for the semiconductor device which is not furnished with the boundary scanning function.