Current–voltage characteristics of AlAs/GaAs/AlAs double barrier resonant tunneling diodes with ferromagnetic p-type (Ga, Mn)As on one side and p-type GaAs on the other have been studied. A series of resonant peaks have been observed in both polarities, i.e., injecting holes from p-type GaAs and from (Ga, Mn)As. When holes are injected from the (Ga, Mn)As side, spontaneous resonant peak splitting has been observed below the ferromagnetic transition temperature of (Ga, Mn)As without magnetic field. The temperature dependence of the splitting is explained by the the spontaneous spin splitting in the valence band of ferromagnetic (Ga, Mn)As. © 1998 American Institute of Physics.