The concentrations and characteristics of major components in inorganic gases and fine particles were measured at the photo and etch cleanroom areas in a Taiwan semiconductor factory. The results showed that the major inorganic gases, as expressed in terms of volume concentration, were NH3 and HF at 7–10 and 4–6 ppbv, respectively. The average PM2.5 mass concentration were 17.52 and 18.23 μg/m3 at the photo and etch areas, respectively, with species of Na+, NH4+, Cl- and SO42- had the highest concentrations in the PM2.5 mass. And the inorganic species account for 56% and 62% of the particulate mass, respectively, at the photo and etch areas. Relatively stronger correlations were observed between NH4+ and SO42- with the correlation coefficient R2 of 0.62 and 0.82, respectively, at the photo and etch areas; this indicates their common source was possibly from the gas to particle formation process. And NH3 was found to co-exist with HF at the etch area due to their common source as process chemicals (NH4OH and HF) in the wet bench. In the predominant NH3-rich environment, ammonia is the basic neutralizing agent to form the ammonium aerosol in a cleanroom.