Rate coefficients for electron attachment to SF4 and SF6 have been measured over the temperature range 300-550 K using a flowing-afterglow Langmuir-probe apparatus. The 300 K rate coefficient for SF4 is 2.5+/-0.6X10(-8) cm(3) s(-1), a value 11 times smaller than the corresponding rate for SF6. The attachment rate coefficients for both SF4 and SF6 are nearly independent of temperature up to 500 K, and decline somewhat at still higher temperatures. SF4- is the only ionic product of attachment to SF4 observed over the entire temperature range. SF6- and SF5- are products of attachment to SF6; an "activation energy" of 0.42+/-0.02 eV is inferred for SF5- production.