IC Testing methods and apparatus

An integrated circuit comprises a device under test and embedded test circuitry. The embedded test circuitry comprises a plurality of process monitoring sensors (14), a threshold circuit (22) for comparing the sensor signals with a threshold window having an upper and a lower limit and a digital interface (17) for outputting the threshold circuit signal. The process monitoring sensors (14) comprise circuitry based on the circuit elements of the device under test. This arrangement enables monitoring of circuit element performance, such as transistor properties, using process monitoring sensors which are embedded with the device under test, so that the same process parameter variations apply to the sensors as to the device under test. The sensors preferably match the physical layout of the device under test