Details of a customized cryogenic test system for use in in situ single-event radiation tests on semiconductor devices at cryogenic temperatures are presented. The lightweight portable system is designed for performing heavy-ion broadbeam single-event radiation testing at different beam facilities. It is designed for use with either liquid nitrogen or liquid helium as cryogens, depending on the desired lower temperature limit. A controlled heating system on the inside allows for single-event radiation tests as a function of temperature. To enable single-event strikes at angles, the device under test can be rotated about a vertical axis without having to break vacuum. Electrical connectivity to the device under test is provided through six fully customizable hermetically sealed connecting ports. The system has been used to conduct single-event tests over temperature on a test circuit fabricated in IBM CMOS 130 nm technology. Single-event transient pulse widths were found to increase by up to 30% as the temperature was varied from - 135 degrees C to + 20 degrees C. Device simulations indicate that single-event-induced parasitic bipolar transistor turn-on in the n-well of PMOS transistors is responsible for the observed increase in pulse widths across the temperature ranges considered. (C) 2010 Elsevier Ltd. All rights reserved.