Gas cabinents are widely used in the semiconductor industry but no evaluation of their performance has been published. This paper describes a technique for testing the performance of these cabinets, and for defining the optimum geometry and exhaust rate. A test protocol was developed that allows one to evaluate the cabinet's ability to remove leaking gas with clearance time used as the critical variable. The test results for a two cylinder gas cabinet indicate that the diffuser and perforated plate inlets perform significantly better than the conventional slotted inlet under all conditions tested. Clearance time for all inlet configurations improves markedly when the flow rate is increased from 0.07 to 0.12 m* h3*s/s (150 to 250 cfm), but little improvement is seen for the diffuser and perforated plate when the flow rate is increased further to 0.17 m³/s (350cfm). Finally, changes in the exhaust configuration had no meaningful effect on clearance time.