The temperature dependence, over the 4.2–100 K range, of the narrow EPR line, labeledX, with an isotropic value ofg= 2.002 has been investigated in a semi‐insulating GaAs:Cr sample. From its Curie‐Weiss behavior, leading to a (T+13.1)−1law, it is concluded that it may result from antiferromagnetic exchange coupled spins, originating from dangling bonds located on extended defects present in the crystal.