Dilute magnetic semiconductors (DMSs) have attracted much attention because of their huge potential applications in spintronics. The simple band-coupling model suggests that isovalent doping of semi-conductors (e.g., Mn-doped II-V semiconductors) should be antiferromagnetic due to the dominant superexchange interaction, which is consistent with experimental observations on most Mn-doped II-VI and Fe-doped III-V semiconductors (FDMSs). However, recently, it has been reported experimentally that some FDMSs are ferromagnetic with a very high Curie temperature (T-C) of over 300 K, but the underlying mechanism is not clear. Here, we reveal that the unusual ferromagnetism in FDMSs originates from a unique p-d coupling-induced band crossing and the resulting charge transfer from anion p to unoccupied Fe 3d orbitals. This result suggests that the ferromagnetism can be more easily realized by Fe doping in III-V semiconductors with high anion p orbital energies, such as GaSb, instead of those with small band gaps, such as InAs. Moreover, we illustrate that the isovalent character guarantees low self-compensation in FDMSs, which sets a major advantage to the realization of high T-C in FDMSs. Our finding can well explain the recent experimental observations and suggests a new avenue for the future design of high-T-C DMSs.