Using telegraph noise measurements on smalln‐ andp‐channel metal‐oxide‐silicon field‐effect transistors, we have measured the entropy change associated with the change of the charge state of individual slow Si/SiO2surface states. Inn‐channel devices we find that the entropy change is positive on electron emission to the silicon conduction band, while inp‐channel devices it is positive on hole emission to the valence band. The results suggest that the slow states in the upper and lower regions of the silicon band gap are of a different type.