Abstract The electrical behaviour of negative temperature coefficient (NTC) thermistors can be expressed by the relationship ϱ=ϱ 25 exp [β( 1 T − 1 298 )] . Good thermistors are thus obtained through the adequate control of the parameters β and ϱ25, which has been achieved in α-Fe2O3 ceramics by a convenient processing. Reducing in nitrogen and then reoxidizing in air has lead to thermistors with good values for β and reasonable ones for ϱ25. The samples consisted then of two phases of polycrystalline ceramics, one of hematite the other of magnetite.