A semiconductor device includes at least one component which is vulnerable to damage during scan testing for a particular input data configuration, and supports a safe mode in which this particular input data configuration is disabled. The semiconductor device also includes a port for receiving an input scan vector for scan testing, and an authorization unit connected to said port. The authorization unit maintains the device in safe mode if an input scan vector does not satisfy at least one predetermined criterion. In one particular implementation, the authorization unit generates a digital signature for the input scan vector, which is then compared to a signature portion included within the input scan vector itself. Scan testing is enabled providing that this comparison finds a match.