The doping effect of aluminum arsenide (AlAs) with 3d (TM = V, Cr, and Mn) of transition metal impurities gives new materials called diluted magnetic semiconductors, which have interesting electronic and magnetic properties for spintronics applications. We have used the full-potential linearized augmented plane wave (FP-LAPW) method to calculate the electronic band structures and magnetic properties of Al_1−xTM_xAs at low concentration x = 0.0625 of transition metal (TM = V, Cr, and Mn) atoms. We have found that the majority-spin states of Al_0.9375TM _0.0625As compounds are metallic due to large p-d hybridization between 3d levels of TM and the 4p levels of As around Fermi level, whereas the minority-spin states have semiconductor character. These compounds exhibit a half-metallic behavior with spin polarization of 100%, where the ferromagnetism is originated from double-exchange mechanism. Therefore, Al_0.9375TM_0.0625As (TM = V, Cr, and Mn) materials seem to be good candidates for spin injection in the field of spintronics applications.