  Creating magnetic semiconductors that work at warm circumstance is still a
great challenge in the physical sciences. Here, we report the discovery of
ferromagnetism in the metal-free perylene diimide semiconductor, whose Curie
temperature is higher than 400 Kelvin. A solvothermal approach is used to
reduce and dissolve the rigid-backbone perylene diimide crystallites, and
radical anion aggregates were fabricated by the subsequent self-assembly and
oxidation process. Magnetic measurements exhibit the ferromagnetic ordering
with the saturated magnetization of 0.48 $\mu_{\rm B}$ per molecule and the
appreciable magnetic anisotropy. X-ray magnetic circular dichroism spectra
suggest the ferromagnetism stems from $\pi$ orbitals of radicals. Our findings
unambitiously demonstrate the long-range ferromagnetic ordering can survive at
room temperature in organic semiconductors, although which are intuitively
regarded to be nonmagnetic.
