The spinning rotor gauge (SRG) used as a vacuum gauge for the range of 10(-4)-1 Pa shows good long-term stability. Therefore it is widely used as a reference standard in calibration services. The calibration constant of the SRG is the effective accommodation coefficient sigma with values around 1. This effective accommodation coefficient of the gas particles to the rotor is considered to be temperature independent for normal operational temperatures of 18-30 degreesC. We have carried out investigations that show that sigma is slightly temperature dependent both for a baked and an unbaked rotor and vacuum system. The temperature range investigated was 16-40 degreesC. Relative changes of sigma varied from 1 x 10(-4) to 4 x 10(-4)/K. As the reason for the temperature dependence we could exclude neither a temperature dependent change of H2O coverage of the rotor nor a temperature dependence of the energy accommodation coefficient. (C) 2003 American Vacuum Society.