Abstract: A fast thermal cycler has a temperature chamber divided into a top, hot compartment heated by heating lamps and a bottom cold compartment cooled by liquid nitrogen, for optimizing thermal cycling rates for devices under test, such as solar cells, for rapid thermal life testing where both compartments use pressurized gaseous nitrogen for thermal conduction and regulation and a motor drive repetitively transports a test device mounted on a panel transiting between the two compartments. The thermal cycler is enhanced by computer control, enabling in-situ electrical testing, fail-safe heating, precision temperature heating and cooling phases, operator alerting and thermal gradient control during the temperature cycling.