Abstract We have applied the full potential linearized augmented plane wave method (FP‐LAPW) within the density functional theory to investigate the structural and electronic properties of the Sc 0.5 In 0.5 N compound in the wurtzite and sodium chloride structures. We have analyzed the relative stability of this ternary compound in the two studied phases. We found that the wurtzite structure is the most stable phase, with the minimum ∼0.14 eV/(unit cell) lower than in the sodium chloride phase. A phase transition from wurtzite to sodium chloride structure was observed, with transition pressure ∼1.9 GPa. Our results predict a direct semiconductor in wurtzite structure and an indirect semiconductor in sodium chloride phase. We investigate the pressure effect on the electronic properties of this ternary compound in the two phases studied. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)