A variety of toxic, corrosive, flammable, pyrophoric, and asphyxiant gases are used in semiconductor manufacturing. Continuous monitoring of such gases has increasingly become a requirement of local and state regulations which are typically based on the Uniform Building Code (Section 911 H-6 occupancy) and Article 80 of the Uniform Fire Code. In addition, the Occupational Safety and Health Act requires each employer to render the workplace free from "recognized hazards causing or likely to cause death or serious physical harm to his employees". Concern for potential employee and community exposure to these gases has made gas detection systems (GDSs) an integral part of safety and health programs in the semiconductor industry. Evaluation of these systems without the benefit of hindsight is difficult since few comparative studies of commercial GDSs have been published (a search of the American Chemical Society Chemical Abstracts - Annual Indexes for the past five years revealed only two papers on this topic)4,5 and most semiconductor companies do not conduct such studies in-house. The first part of this paper reviews several types of GDSs with respect to their principal of operation, sensitivity, selectivity, response time and cost. The GDS types discussed are those based on electrochemical sensors, semiconductor sensors, paper-tape detectors, flame-emission spectrometry (FES), Fourier-Transform Infrared Spectrometry (FTIR), and mass spectrometry (MS). The second part of the paper describes the results of a mail survey of Semiconductor Safety Association (SSA) members to assess GDS utilization and performance in the in- dustry. Respondents provided information on GDS makes/models used, user satisfaction, gases used and monitored, areas monitored, frequency of false alarms, alarm locations, frequency of calibration and maintenance, and other characteristics.