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Pressures in UHV and XHV have been successfully measured using a quadrupole mass spectrometer (QMS) with a Spindt-type field emitter array (FEA) as the electron source. However, two problems remained to be resolved: a reduction in the small amount of outgassing from FEA, and an elimination of ESD ions. Outgassing from FEA became negligible after degassing at 400 °C for 5 h in a vacuum of 10 −6 Pa. Thus, the degassed FEA allowed us to measure the pressure in UHV and XHV with little disturbance from the vacuum conditions. After that, the ESD effect on the partial pressure measurement with QMS was investigated through the use of the time-of-flight (TOF) technique. The ESD components for H 2 and CO were small compared with the gas-phase ions. However, mass 16 had a large ESD peak in the TOF spectrum as well as mass 19. The gas-phase peak for H 2 was proportional to the pressure, although the ESD component was not only a function of the pressure. The area measurement under the gas-phase peak in the TOF spectra was useful in measuring pressures of less than 10 −10 Pa.