Abstract: A high-speed test system for semiconductor integrated circuits utilizes electro-optic sampling techniques to perform tests at data rates up to 1.2 Gb/s. The receiver portion of the tester has a 4.5 GHz bandwidth and can perform ECL level functional test with one sampling pulse per vector. A device under test is positioned in a test head with an electro-optic birefringent crystal sensor positioned below the device under test to minimize signal path length. A system control unit includes a Nd: YAG modelocked laser which generates optical pulses, and optical transmission means directs the optical pulses to an array of reflective contacts on the sensor. The sensor functions as a Pockels cell with the electric field in the crystal sensor due to voltages on the array of contacts changing the transmission of polarized light through the crystal. Reflected pulses are received and converted to electrical signals indicative of the voltages on the array of contacts on the electro-optic sensor.