We find the thermally induced defects in undoped hydrogenated amorphous silicon carbon (a
H) by electron spin resonance and conductivity measurements. The equilibrium temperature (Te
) determined from the annealing temperature‐dependent density of dangling bonds after fast cooling decreases with increasing C content, from 190 °C for hydrogenated amorphous silicon to 150 °C for a
H. Possible microscopic mechanisms for the observed thermally induced defects in a
H alloys are discussed.